MIL-003: Step 2 - New flash cards

Review record RC-025 (Go, autonomous mode, not independent).

Task: MIL-003#1
Task: MIL-003#2
Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

docs/artifact-registry.md

@@ -25,7 +25,7 @@ document of a type. `Primary File` may contain a glob (e.g.
 | DCD | Design Class Diagram | docs/dcd.md | 002 |
 | DICT | Domain Dictionary | docs/dictionary.md | 002 |
 | ADR | Architecture Decision Record | docs/adr/adr-NNNN-*.md | 0004 |
-| RC | SQA Review Record | docs/sqa/reviews/rc-*.md | 025 |
+| RC | SQA Review Record | docs/sqa/reviews/rc-*.md | 026 |
 | TM | Traceability Matrix | docs/sqa/traceability-matrix.md | 002 |
 
 ## Languages

docs/sqa/reviews/rc-025-py-mil-003.md

@@ -0,0 +1,63 @@
+# RC-025: Review of PY-MIL-003
+
+## Metadata
+| Key | Value |
+| --- | --- |
+| ID | RC-025 |
+| CrossReference | [PY-MIL-003], [QC-PY-001] |
+
+## Version History
+| Date | Status | Author | Reviewer | Change | Commit |
+| --- | --- | --- | --- | --- | --- |
+| 2026-10-14 | Accepted | Jens Tirsvad Nielsen | AI as stand-in for S01 | Initial version | pending |
+
+---
+
+## Artifact Under Review
+
+- Instance reviewed: [PY-MIL-003]
+- Checklist used: [QC-PY-001]
+- Scope: full review
+- Language and domain: n/a (technical type)
+- Language reviewer: none
+- Mode: autonomous, not independent (reviewer is `AI as stand-in for S01`)
+
+## Checklist Results
+
+| # | Criterion | Status | Evidence/Notes |
+| --- | --- | --- | --- |
+| 1 | Packages, modules, functions, variables, classes and constants follow PEP 8 casing (`snake_case`, `PascalCase`, `UPPER_SNAKE`) | Pass | Packages, modules, classes and functions follow PEP 8 casing; ruff rule set N passes. |
+| 2 | Names state purpose in the domain's language; no unexplained abbreviations, no single-letter names outside tiny scopes | Pass | Names state purpose in the dictionary's IT terms (`Deck`, `Vocabulary`, `StudySession`, `CardDto`). |
+| 3 | Code is produced by the project's formatter and passes its linter with no unexplained suppressions | Pass | `ruff check` and `ruff format --check` pass on 43 files with no suppressions. |
+| 4 | Every function and method signature is type-annotated, including `-> None` | Pass | Every signature is annotated; `mypy --strict` passes on 31 source files. |
+| 5 | No bare `except:`, no swallowed exceptions; specific exceptions are raised and the cause is kept (`raise ... from`) | Pass | `read_word_list` raises `VocabularyNotFoundError` with `from` to keep the cause; no bare or swallowed exception; `Deck.remove` raises `ValueError` (not in OC-001, a deviation recorded here). |
+| 6 | No mutable default arguments and no shadowed builtins | Pass | No mutable default arguments; no builtin shadowed (`Card`, `Deck` do not shadow). |
+| 7 | Files, locks and connections are managed with context managers | Pass | The CSV file is opened with `with` in `read_word_list`. |
+| 8 | Public modules, classes and functions have docstrings that say what, not how | Pass | Public modules, classes and functions have Doxygen docstrings; `doxygen Doxyfile` ends with 0 warnings. |
+| 9 | Logging uses `logging`, not `print`; no secrets or personal data in log output | Pass | No `print`; `app.main` logs errors with `logging`; no personal data logged. |
+| 10 | Classes and operations trace to the Design Class Diagram they implement; deviations are recorded | Pass | Classes and operations are those of DCD-001 (`Card`, `LanguagePair`, `Vocabulary`, `Deck`, `StudySession`, `CardDto`, `CsvVocabularyRepository`, view and view model). Deviations: `Deck.remove` raises `ValueError` when the card is absent; `read_word_list` is a shared function behind both CSV repositories, as MIL-005 task 1 requires. |
+| 11 | Tests exist for new behaviour, are named for the behaviour, and do not depend on order or the network | Pass | 66 tests (unit by layer, integration on the real `data/ms-da.csv`, e2e on the real window) named for behaviour; none uses the network or depends on order. |
+| 12 | Type checker runs in strict mode without errors; `Any` is justified in a comment | Pass | `mypy --strict` reports no issue; no `Any`. |
+| 13 | Dependencies are declared and pinned in the project's dependency file, none unused | Pass | `dependencies` stays empty; `csv`, `random` and `pathlib` are standard library (ADR-0001). |
+| 14 | Each piece of knowledge (a business rule, constant, format, validation or query) is defined in one place; code is merged only where it expresses the same knowledge, not where it merely looks alike | Pass | The CSV format, encoding and delimiter are defined once in `constants.py` and `read_word_list`; the draw rule is only in `Deck.draw`. |
+| 15 | Imports point inward: business-rule modules import no framework, database, UI or delivery-mechanism code, and there are no import cycles | Pass | `lint-imports` reports `Layers point inward` kept; a grep finds no `tkinter`, `csv` or `random` import in `domain` or `application`. |
+| 16 | SOLID holds: a class or module has one reason to change; new behaviour is added by extension, not by editing a type test in several places; subclasses honour the contract of their base; protocols are narrow; high-level code depends on protocols or abstract types and receives its implementations | Pass | One reason to change per class; the choice function is injected into `StudySession` and `Deck.draw`, and the repository is a Protocol that the use case receives. |
+| 17 | Source is laid out in the layers and folders of the clean architecture folder structure (`domain`, `application`, `infrastructure`, `presentation` packages under `src/`, and `unit`, `integration` and `e2e` under `tests/`), in `snake_case`, and imports between the layers point inward | Pass | Source is in `domain`, `application`, `infrastructure`, `presentation` with the sub-folders of the clean-architecture skill; tests in `unit`, `integration`, `e2e`. |
+| 18 | File and folder names are English, contain no space and no character outside letters, digits, `-`, `_` and `.`, and follow the casing of the language for files | Pass | File and folder names are English snake_case, no space. |
+
+## Overall Verdict
+
+Go — every Mandatory criterion passes. Reviewed by AI as stand-in for S01; not independent of the author.
+
+Milestone MIL-003 Go criteria: 1 integration test reads 1000 cards, pair ms/da; 2 missing header, bad row and missing file raise `VocabularyFormatError`/`VocabularyNotFoundError` (unit tests); 3 a press shows a different card when two or more exist and the same when one (unit tests); 4 blank lines are ignored (unit test); 5 no `tkinter`, `csv` or `random` import in domain/application (grep, empty); 6 this record and `pytest` 66 passed. A manual smoke run on the real file showed a new word after a press. All Go.
+
+## Action Items
+
+| Action | Owner | Due |
+| --- | --- | --- |
+| none | - | - |
+
+---
+
+[PY-MIL-003]: ../../../src/flash_card
+[QC-PY-001]: ../../../framework/qc/code/qc-programming-python.md

docs/sqa/traceability-matrix.md

@@ -47,6 +47,7 @@ updated whenever an artifact instance is created or reviewed.
 | MIL-007 | Milestone / Gateway | en | it | BC-001, PP-001 | tasks of MIL-007 | [RC-022] |
 | PY-MIL-001 | Python Source Code | - | - | DCD-001, ADR-0002 | - | [RC-023] |
 | PY-MIL-002 | Python Source Code | - | - | DCD-001, ADR-0002 | - | [RC-024] |
+| PY-MIL-003 | Python Source Code | - | - | DCD-001, ADR-0002 | - | [RC-025] |
 
 ## Coverage Notes
 
@@ -105,3 +106,5 @@ updated whenever an artifact instance is created or reviewed.
 [c3fbcbc]: https://git.tirsystem.com/Tirsvad-Udemy-100-days-of-code/031-flash-card/commit/c3fbcbcfaf799e0ae34aed7e14d3bc8a62f03db3
 [RC-024]: ./reviews/rc-024-py-mil-002.md
 [PY-MIL-002]: ../../src/flash_card
+[RC-025]: ./reviews/rc-025-py-mil-003.md
+[PY-MIL-003]: ../../src/flash_card

src/flash_card/application/dto/__init__.py

@@ -0,0 +1,5 @@
+"""Application data transfer objects.
+
+@file __init__.py
+@brief Holds the plain data that crosses to the presentation layer.
+"""

src/flash_card/application/dto/card_dto.py

@@ -0,0 +1,21 @@
+"""Card data for the presentation layer.
+
+@file card_dto.py
+@brief The CardDto: a card as plain text.
+"""
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class CardDto:
+    """A card as plain data."""
+
+    ## @brief Word on the card front.
+    front_text: str
+    ## @brief Translation on the card back.
+    back_text: str
+    ## @brief Language code of the front.
+    front_language: str
+    ## @brief Language code of the back.
+    back_language: str

src/flash_card/application/use_cases/__init__.py

@@ -0,0 +1,5 @@
+"""Application use cases.
+
+@file __init__.py
+@brief Holds the use cases of the flash card program.
+"""

src/flash_card/application/use_cases/open_study_session.py

@@ -0,0 +1,27 @@
+"""Start a study session.
+
+@file open_study_session.py
+@brief The open_study_session use case.
+"""
+
+from collections.abc import Callable, Sequence
+
+from flash_card.application.use_cases.study_session import StudySession
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.deck import Deck
+from flash_card.domain.repositories.vocabulary_repository import VocabularyRepository
+
+
+def open_study_session(
+    vocabulary_repository: VocabularyRepository,
+    choose: Callable[[Sequence[Card]], Card],
+) -> StudySession:
+    """Load the word list and build a session over all its cards.
+
+    @param vocabulary_repository Source of the word list.
+    @param choose Picks one card from a non-empty sequence.
+    @return The new session.
+    @throws VocabularyError When the word list cannot be loaded.
+    """
+    deck = Deck.from_vocabulary(vocabulary_repository.load())
+    return StudySession(deck, choose)

src/flash_card/application/use_cases/study_session.py

@@ -0,0 +1,66 @@
+"""One study session.
+
+@file study_session.py
+@brief The StudySession use case: draws the cards the user studies.
+"""
+
+from collections.abc import Callable, Sequence
+
+from flash_card.application.dto.card_dto import CardDto
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.deck import Deck
+
+
+class StudySession:
+    """Draws cards from a deck, one after another."""
+
+    def __init__(self, deck: Deck, choose: Callable[[Sequence[Card]], Card]) -> None:
+        """Create a session.
+
+        @param deck The cards still to learn.
+        @param choose Picks one card from a non-empty sequence.
+        """
+        ## @brief The cards still to learn.
+        self._deck = deck
+        ## @brief Picks one card from a non-empty sequence.
+        self._choose = choose
+        ## @brief The card shown now, or None.
+        self._current: Card | None = None
+
+    @property
+    def current_card(self) -> CardDto | None:
+        """Return the card shown now.
+
+        @return The card, or None before the first draw or when none is left.
+        """
+        return self._to_dto(self._current)
+
+    @property
+    def remaining(self) -> int:
+        """Return the number of cards still to learn.
+
+        @return The card count.
+        """
+        return len(self._deck)
+
+    def next_card(self) -> CardDto | None:
+        """Draw the next card, different from the current one when possible.
+
+        @return The new card, or None when the deck is empty.
+        """
+        if self._deck.is_empty:
+            self._current = None
+            return None
+        self._current = self._deck.draw(self._choose, exclude=self._current)
+        return self._to_dto(self._current)
+
+    def _to_dto(self, card: Card | None) -> CardDto | None:
+        """Map a card to its DTO.
+
+        @param card The card, or None.
+        @return The DTO, or None when there is no card.
+        """
+        if card is None:
+            return None
+        pair = self._deck.language_pair
+        return CardDto(card.front, card.back, pair.front_code, pair.back_code)

src/flash_card/constants.py

@@ -42,15 +42,11 @@ BACK_TEXT_COLOR: Final[str] = "white"
 LANGUAGE_NAMES: Final[Mapping[str, str]] = {"ms": "Malay", "da": "Danish"}
 ## @brief Message shown when no word is left to learn.
 FINISHED_MESSAGE: Final[str] = "Nothing left to learn"
-## @brief Language name shown before the first card.
-PLACEHOLDER_LANGUAGE_NAME: Final[str] = "Malay"
-## @brief Word shown before the first card.
-PLACEHOLDER_WORD: Final[str] = "kata"
 
 ## @brief Delimiter of the CSV files.
 CSV_DELIMITER: Final[str] = ";"
-## @brief Encoding of the CSV files.
-CSV_ENCODING: Final[str] = "utf-8"
+## @brief Encoding of the CSV files; drops a leading byte order mark.
+CSV_ENCODING: Final[str] = "utf-8-sig"
 ## @brief File name of the vocabulary.
 VOCABULARY_FILE_NAME: Final[str] = "ms-da.csv"
 ## @brief File name of the words still to learn.

src/flash_card/domain/entities/__init__.py

@@ -0,0 +1,5 @@
+"""Domain entities.
+
+@file __init__.py
+@brief Holds the entities of the flash card program.
+"""

src/flash_card/domain/entities/card.py

@@ -0,0 +1,17 @@
+"""A flash card.
+
+@file card.py
+@brief The Card entity: a word and its translation.
+"""
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class Card:
+    """A word and its translation."""
+
+    ## @brief The word in the front language.
+    front: str
+    ## @brief The translation in the back language.
+    back: str

src/flash_card/domain/entities/deck.py

@@ -0,0 +1,95 @@
+"""The cards still to learn.
+
+@file deck.py
+@brief The Deck entity: holds cards, draws one and removes one.
+"""
+
+from collections.abc import Callable, Iterable, Sequence
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.vocabulary import Vocabulary
+from flash_card.domain.errors.vocabulary_errors import EmptyDeckError
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+
+class Deck:
+    """The cards still to learn, of one language pair."""
+
+    def __init__(self, language_pair: LanguagePair, cards: Iterable[Card]) -> None:
+        """Create a deck.
+
+        @param language_pair The languages of the cards.
+        @param cards The cards of the deck.
+        """
+        ## @brief The languages of the cards.
+        self._language_pair = language_pair
+        ## @brief The cards still in the deck.
+        self._cards = list(cards)
+
+    @classmethod
+    def from_vocabulary(cls, vocabulary: Vocabulary) -> "Deck":
+        """Create a deck holding every card of a vocabulary.
+
+        @param vocabulary The delivered word list.
+        @return A new deck.
+        """
+        return cls(vocabulary.language_pair, vocabulary.cards)
+
+    @property
+    def language_pair(self) -> LanguagePair:
+        """Return the languages of the cards.
+
+        @return The language pair.
+        """
+        return self._language_pair
+
+    @property
+    def cards(self) -> tuple[Card, ...]:
+        """Return a copy of the cards.
+
+        @return The cards in deck order.
+        """
+        return tuple(self._cards)
+
+    @property
+    def is_empty(self) -> bool:
+        """Tell whether the deck has no card.
+
+        @return True when no card is left.
+        """
+        return not self._cards
+
+    def __len__(self) -> int:
+        """Return the number of cards.
+
+        @return The card count.
+        """
+        return len(self._cards)
+
+    def draw(
+        self,
+        choose: Callable[[Sequence[Card]], Card],
+        exclude: Card | None = None,
+    ) -> Card:
+        """Pick a card without removing it.
+
+        The pick avoids the excluded card when another card exists.
+
+        @param choose Picks one card from a non-empty sequence.
+        @param exclude A card to avoid, usually the one shown now.
+        @return The picked card.
+        @throws EmptyDeckError When the deck has no card.
+        """
+        if not self._cards:
+            raise EmptyDeckError("cannot draw from an empty deck")
+        others = [card for card in self._cards if card != exclude]
+        return choose(others or self._cards)
+
+    def remove(self, card: Card) -> None:
+        """Remove the first card equal to the given one.
+
+        @param card The card to remove.
+        @return Nothing.
+        @throws ValueError When the deck holds no such card.
+        """
+        self._cards.remove(card)

src/flash_card/domain/entities/vocabulary.py

@@ -0,0 +1,20 @@
+"""The delivered word list.
+
+@file vocabulary.py
+@brief The Vocabulary entity: all cards of a language pair.
+"""
+
+from dataclasses import dataclass
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+
+@dataclass(frozen=True, slots=True)
+class Vocabulary:
+    """All cards of a language pair as delivered."""
+
+    ## @brief The languages of the cards.
+    language_pair: LanguagePair
+    ## @brief The cards in file order.
+    cards: tuple[Card, ...]

src/flash_card/domain/errors/__init__.py

@@ -0,0 +1,5 @@
+"""Domain errors.
+
+@file __init__.py
+@brief Holds the errors the domain rules raise.
+"""

src/flash_card/domain/errors/vocabulary_errors.py

@@ -0,0 +1,21 @@
+"""Errors of the vocabulary and the deck.
+
+@file vocabulary_errors.py
+@brief The VocabularyError hierarchy.
+"""
+
+
+class VocabularyError(Exception):
+    """Base of every error about the word list or the deck."""
+
+
+class VocabularyFormatError(VocabularyError):
+    """The word list is not in the expected format."""
+
+
+class VocabularyNotFoundError(VocabularyError):
+    """The word list does not exist."""
+
+
+class EmptyDeckError(VocabularyError):
+    """A card was drawn from a deck with no card."""

src/flash_card/domain/repositories/__init__.py

@@ -0,0 +1,5 @@
+"""Domain repository ports.
+
+@file __init__.py
+@brief Holds the repository interfaces of the domain.
+"""

src/flash_card/domain/repositories/vocabulary_repository.py

@@ -0,0 +1,21 @@
+"""Port to the delivered word list.
+
+@file vocabulary_repository.py
+@brief The VocabularyRepository interface.
+"""
+
+from typing import Protocol
+
+from flash_card.domain.entities.vocabulary import Vocabulary
+
+
+class VocabularyRepository(Protocol):
+    """Source of the delivered word list."""
+
+    def load(self) -> Vocabulary:
+        """Load the delivered word list.
+
+        @return The vocabulary.
+        @throws VocabularyError When the word list cannot be loaded.
+        """
+        ...

src/flash_card/domain/value_objects/__init__.py

@@ -0,0 +1,5 @@
+"""Domain value objects.
+
+@file __init__.py
+@brief Holds the immutable value objects of the domain.
+"""

src/flash_card/domain/value_objects/language_pair.py

@@ -0,0 +1,17 @@
+"""The two languages of a word list.
+
+@file language_pair.py
+@brief The LanguagePair value object.
+"""
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, slots=True)
+class LanguagePair:
+    """The language codes of the front and the back of the cards."""
+
+    ## @brief Language code of the card front.
+    front_code: str
+    ## @brief Language code of the card back.
+    back_code: str

src/flash_card/infrastructure/persistence/__init__.py

@@ -0,0 +1,5 @@
+"""Persistence adapters.
+
+@file __init__.py
+@brief Holds the adapters that read and write files.
+"""

src/flash_card/infrastructure/persistence/csv_vocabulary_repository.py

@@ -0,0 +1,35 @@
+"""CSV implementation of the vocabulary port.
+
+@file csv_vocabulary_repository.py
+@brief The CsvVocabularyRepository adapter.
+"""
+
+from pathlib import Path
+
+from flash_card.domain.entities.vocabulary import Vocabulary
+from flash_card.domain.errors.vocabulary_errors import VocabularyFormatError
+from flash_card.infrastructure.persistence.csv_word_list import read_word_list
+
+
+class CsvVocabularyRepository:
+    """Loads the delivered word list from a CSV file."""
+
+    def __init__(self, path: Path) -> None:
+        """Create the repository.
+
+        @param path The word list file.
+        """
+        ## @brief The word list file.
+        self._path = path
+
+    def load(self) -> Vocabulary:
+        """Load the word list.
+
+        @return The vocabulary.
+        @throws VocabularyNotFoundError When the file does not exist.
+        @throws VocabularyFormatError When the file is malformed or has no card.
+        """
+        pair, cards = read_word_list(self._path)
+        if not cards:
+            raise VocabularyFormatError(f"{self._path}: word list has no card")
+        return Vocabulary(pair, cards)

src/flash_card/infrastructure/persistence/csv_word_list.py

@@ -0,0 +1,86 @@
+"""Reading of the word list CSV file.
+
+@file csv_word_list.py
+@brief Reads a semicolon separated word list with a language code header.
+"""
+
+import csv
+from pathlib import Path
+
+from flash_card.constants import CSV_DELIMITER, CSV_ENCODING
+from flash_card.domain.entities.card import Card
+from flash_card.domain.errors.vocabulary_errors import (
+    VocabularyFormatError,
+    VocabularyNotFoundError,
+)
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+## @brief Number of cells in the header and in every card row.
+_CELLS_PER_ROW = 2
+
+
+def _format_error(path: Path, line: int, reason: str) -> VocabularyFormatError:
+    """Build a format error naming the file and line.
+
+    @param path The file read.
+    @param line The line number of the fault.
+    @param reason What is wrong.
+    @return The error to raise.
+    """
+    return VocabularyFormatError(f"{path}, line {line}: {reason}")
+
+
+def _parse_header(path: Path, line: int, row: list[str]) -> LanguagePair:
+    """Parse the header row.
+
+    @param path The file read.
+    @param line The line number of the row.
+    @param row The cells of the row.
+    @return The language pair.
+    @throws VocabularyFormatError When the header is not two codes.
+    """
+    cells = [cell.strip() for cell in row]
+    if len(cells) != _CELLS_PER_ROW or not all(cells):
+        raise _format_error(path, line, "header must hold two language codes")
+    return LanguagePair(cells[0], cells[1])
+
+
+def _parse_card(path: Path, line: int, row: list[str]) -> Card:
+    """Parse a card row.
+
+    @param path The file read.
+    @param line The line number of the row.
+    @param row The cells of the row.
+    @return The card.
+    @throws VocabularyFormatError When the row is not two cells.
+    """
+    if len(row) != _CELLS_PER_ROW:
+        raise _format_error(path, line, "row must hold exactly two cells")
+    return Card(row[0].strip(), row[1].strip())
+
+
+def read_word_list(path: Path) -> tuple[LanguagePair, tuple[Card, ...]]:
+    """Read a word list file.
+
+    @param path The CSV file: a header of two language codes, then one card a row.
+    @return The language pair and the cards in file order.
+    @throws VocabularyNotFoundError When the file does not exist.
+    @throws VocabularyFormatError When the file is empty or a row is malformed.
+    """
+    pair: LanguagePair | None = None
+    cards: list[Card] = []
+    try:
+        with path.open(encoding=CSV_ENCODING, newline="") as file:
+            reader = csv.reader(file, delimiter=CSV_DELIMITER)
+            for row in reader:
+                if not any(cell.strip() for cell in row):
+                    continue
+                if pair is None:
+                    pair = _parse_header(path, reader.line_num, row)
+                else:
+                    cards.append(_parse_card(path, reader.line_num, row))
+    except FileNotFoundError as error:
+        raise VocabularyNotFoundError(f"word list not found: {path}") from error
+    if pair is None:
+        raise _format_error(path, 1, "file is empty")
+    return pair, tuple(cards)

src/flash_card/presentation/app.py

@@ -4,33 +4,66 @@
 @brief Creates the window, its view model and view, and runs the main loop.
 """
 
+import argparse
+import logging
+import random
 import tkinter as tk
 from collections.abc import Sequence
+from pathlib import Path
 from typing import NoReturn
 
+from flash_card.application.use_cases.open_study_session import open_study_session
+from flash_card.constants import DEFAULT_DATA_DIR, VOCABULARY_FILE_NAME
+from flash_card.domain.errors.vocabulary_errors import VocabularyError
+from flash_card.infrastructure.persistence.csv_vocabulary_repository import (
+    CsvVocabularyRepository,
+)
 from flash_card.presentation.features.flash_card.flash_card_view import FlashCardView
 from flash_card.presentation.features.flash_card.flash_card_view_model import (
     FlashCardViewModel,
 )
 
+## @brief Logger of the entry point.
+_logger = logging.getLogger(__name__)
 
-def create_application() -> tuple[tk.Tk, FlashCardView]:
+
+def create_application(
+    data_dir: Path | None = None,
+) -> tuple[tk.Tk, FlashCardView]:
     """Create the root window and the flash card view.
 
+    @param data_dir Folder of the data files, or None for the default folder.
     @return The root window and the view built on it.
+    @throws VocabularyError When the word list cannot be loaded.
     """
+    folder = DEFAULT_DATA_DIR if data_dir is None else data_dir
+    repository = CsvVocabularyRepository(folder / VOCABULARY_FILE_NAME)
+    session = open_study_session(repository, random.choice)
+    view_model = FlashCardViewModel(session)
     root = tk.Tk()
-    view = FlashCardView(root, FlashCardViewModel())
+    view = FlashCardView(root, view_model)
     return root, view
 
 
 def main(argv: Sequence[str] | None = None) -> int:
     """Run the program and return its exit code.
 
-    @param argv Command line arguments, or None for none.
-    @return The exit code, 0 on success.
+    @param argv Command line arguments, or None for those of the process.
+    @return The exit code, 0 on success and 1 when the word list is unusable.
     """
-    root, _view = create_application()
+    parser = argparse.ArgumentParser(description="Flash card program.")
+    parser.add_argument(
+        "--data-dir",
+        type=Path,
+        default=DEFAULT_DATA_DIR,
+        help="folder of the data files",
+    )
+    args = parser.parse_args(argv)
+    try:
+        root, _view = create_application(args.data_dir)
+    except VocabularyError as error:
+        _logger.error("%s", error)
+        return 1
     root.mainloop()
     return 0
 

src/flash_card/presentation/features/flash_card/flash_card_view.py

@@ -84,11 +84,30 @@ class FlashCardView:
 
         ## @brief Button for a word the user does not know.
         self.wrong_button = tk.Button(
-            root, image=self._wrong_image, highlightthickness=0, bd=0
+            root,
+            image=self._wrong_image,
+            highlightthickness=0,
+            bd=0,
+            command=self.next_card,
         )
         self.wrong_button.grid(row=1, column=0)
         ## @brief Button for a word the user knows.
         self.right_button = tk.Button(
-            root, image=self._right_image, highlightthickness=0, bd=0
+            root,
+            image=self._right_image,
+            highlightthickness=0,
+            bd=0,
+            command=self.next_card,
         )
         self.right_button.grid(row=1, column=1)
+
+    def next_card(self) -> None:
+        """Show the next card.
+
+        @return Nothing.
+        """
+        self._view_model.next_card()
+        self.canvas.itemconfig(
+            self.language_text_id, text=self._view_model.language_name
+        )
+        self.canvas.itemconfig(self.word_text_id, text=self._view_model.text)

src/flash_card/presentation/features/flash_card/flash_card_view_model.py

@@ -4,24 +4,66 @@
 @brief Exposes the texts shown on the card; free of any Tkinter import.
 """
 
-from flash_card.constants import PLACEHOLDER_LANGUAGE_NAME, PLACEHOLDER_WORD
+from collections.abc import Mapping
+
+from flash_card.application.dto.card_dto import CardDto
+from flash_card.application.use_cases.study_session import StudySession
+from flash_card.constants import FINISHED_MESSAGE, LANGUAGE_NAMES
 
 
 class FlashCardViewModel:
     """Data the flash card view shows."""
 
+    def __init__(
+        self,
+        session: StudySession,
+        language_names: Mapping[str, str] = LANGUAGE_NAMES,
+    ) -> None:
+        """Create the view model and draw the first card.
+
+        @param session The study session that supplies the cards.
+        @param language_names Display names by language code.
+        """
+        ## @brief The study session that supplies the cards.
+        self._session = session
+        ## @brief Display names by language code.
+        self._language_names = language_names
+        ## @brief The card shown now, or None when none is left.
+        self._card: CardDto | None = session.next_card()
+
+    @property
+    def is_finished(self) -> bool:
+        """Tell whether no card is left to show.
+
+        @return True when there is no card.
+        """
+        return self._card is None
+
     @property
     def language_name(self) -> str:
         """Return the language name shown on the card.
 
-        @return The display name of the language.
+        @return The display name of the front language, upper case code when
+            unknown, or an empty string when no card is left.
         """
-        return PLACEHOLDER_LANGUAGE_NAME
+        if self._card is None:
+            return ""
+        code = self._card.front_language
+        return self._language_names.get(code, code.upper())
 
     @property
     def text(self) -> str:
         """Return the word shown on the card.
 
-        @return The word text.
+        @return The front text, or the finished message when no card is left.
         """
-        return PLACEHOLDER_WORD
+        if self._card is None:
+            return FINISHED_MESSAGE
+        return self._card.front_text
+
+    def next_card(self) -> None:
+        """Draw the next card.
+
+        @return Nothing.
+        """
+        self._card = self._session.next_card()

tests/e2e/test_flash_card_window.py

@@ -5,27 +5,47 @@
 """
 
 import tkinter as tk
-from collections.abc import Iterator
+from collections.abc import Iterator, Sequence
 
 import pytest
 
+from flash_card.application.use_cases.study_session import StudySession
 from flash_card.constants import (
     BACKGROUND_COLOR,
     CARD_HEIGHT,
     CARD_WIDTH,
     FRONT_TEXT_COLOR,
     LANGUAGE_FONT,
-    PLACEHOLDER_LANGUAGE_NAME,
-    PLACEHOLDER_WORD,
     WINDOW_PADDING,
     WINDOW_TITLE,
     WORD_FONT,
 )
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.deck import Deck
+from flash_card.domain.value_objects.language_pair import LanguagePair
 from flash_card.presentation.features.flash_card.flash_card_view import FlashCardView
 from flash_card.presentation.features.flash_card.flash_card_view_model import (
     FlashCardViewModel,
 )
 
+CARDS = (Card("aku", "mig"), Card("kau", "du"), Card("ini", "denne"))
+
+
+def _first(cards: Sequence[Card]) -> Card:
+    return cards[0]
+
+
+def _build_view(root: tk.Tk) -> FlashCardView:
+    deck = Deck(LanguagePair("ms", "da"), CARDS)
+    return FlashCardView(root, FlashCardViewModel(StudySession(deck, _first)))
+
+
+def _shown(view: FlashCardView) -> tuple[str, str]:
+    return (
+        str(view.canvas.itemcget(view.language_text_id, "text")),
+        str(view.canvas.itemcget(view.word_text_id, "text")),
+    )
+
 
 @pytest.fixture(scope="module")
 def window() -> Iterator[tuple[tk.Tk, FlashCardView]]:
@@ -35,7 +55,7 @@ def window() -> Iterator[tuple[tk.Tk, FlashCardView]]:
         root = tk.Tk()
     except tk.TclError:
         pytest.skip("no display available for Tk")
-    view = FlashCardView(root, FlashCardViewModel())
+    view = _build_view(root)
     root.update_idletasks()
     yield root, view
     root.destroy()
@@ -72,14 +92,14 @@ def test_canvas_holds_one_image_and_two_texts(
     assert len(types) == 3
 
 
-def test_texts_show_placeholders_with_font_and_colour(
+def test_texts_show_first_card_with_font_and_colour(
     window: tuple[tk.Tk, FlashCardView],
 ) -> None:
     _root, view = window
     canvas = view.canvas
     expected = [
-        (view.language_text_id, PLACEHOLDER_LANGUAGE_NAME, LANGUAGE_FONT),
-        (view.word_text_id, PLACEHOLDER_WORD, WORD_FONT),
+        (view.language_text_id, "Malay", LANGUAGE_FONT),
+        (view.word_text_id, "aku", WORD_FONT),
     ]
     for item, text, font in expected:
         assert canvas.itemcget(item, "text") == text
@@ -101,5 +121,16 @@ def test_buttons_sit_in_row_one_with_their_images(
     assert wrong_image
     assert right_image
     assert wrong_image != right_image
-    assert not str(view.wrong_button.cget("command"))
-    assert not str(view.right_button.cget("command"))
+    assert str(view.wrong_button.cget("command"))
+    assert str(view.right_button.cget("command"))
+
+
+def test_each_button_press_shows_next_card(
+    window: tuple[tk.Tk, FlashCardView],
+) -> None:
+    _root, view = window
+    assert _shown(view) == ("Malay", "aku")
+    view.wrong_button.invoke()
+    assert _shown(view) == ("Malay", "kau")
+    view.right_button.invoke()
+    assert _shown(view) == ("Malay", "aku")

tests/integration/test_vocabulary_file.py

@@ -0,0 +1,31 @@
+"""Integration tests of the word list reader on the delivered file."""
+
+from flash_card.application.use_cases.open_study_session import open_study_session
+from flash_card.constants import DEFAULT_DATA_DIR, VOCABULARY_FILE_NAME
+from flash_card.domain.entities.card import Card
+from flash_card.domain.value_objects.language_pair import LanguagePair
+from flash_card.infrastructure.persistence.csv_vocabulary_repository import (
+    CsvVocabularyRepository,
+)
+from flash_card.infrastructure.persistence.csv_word_list import read_word_list
+
+PATH = DEFAULT_DATA_DIR / VOCABULARY_FILE_NAME
+
+
+def test_read_word_list_reads_real_file() -> None:
+    pair, cards = read_word_list(PATH)
+    assert pair == LanguagePair("ms", "da")
+    assert len(cards) == 1000
+    assert cards[0] == Card("aku", "mig")
+
+
+def test_open_study_session_yields_card_from_real_file() -> None:
+    repository = CsvVocabularyRepository(PATH)
+    cards = repository.load().cards
+    session = open_study_session(repository, lambda candidates: candidates[0])
+
+    card = session.next_card()
+
+    assert card is not None
+    assert Card(card.front_text, card.back_text) in cards
+    assert (card.front_language, card.back_language) == ("ms", "da")

tests/unit/application/test_open_study_session.py

@@ -0,0 +1,44 @@
+"""Tests of the open_study_session use case."""
+
+from collections.abc import Sequence
+
+import pytest
+
+from flash_card.application.dto.card_dto import CardDto
+from flash_card.application.use_cases.open_study_session import open_study_session
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.vocabulary import Vocabulary
+from flash_card.domain.errors.vocabulary_errors import VocabularyNotFoundError
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+
+class _FakeRepository:
+    def __init__(self, vocabulary: Vocabulary) -> None:
+        self._vocabulary = vocabulary
+
+    def load(self) -> Vocabulary:
+        return self._vocabulary
+
+
+class _MissingRepository:
+    def load(self) -> Vocabulary:
+        raise VocabularyNotFoundError("missing")
+
+
+def _first(cards: Sequence[Card]) -> Card:
+    return cards[0]
+
+
+def test_open_study_session_builds_session_over_all_cards() -> None:
+    cards = (Card("aku", "mig"), Card("kau", "du"))
+    repository = _FakeRepository(Vocabulary(LanguagePair("ms", "da"), cards))
+
+    session = open_study_session(repository, _first)
+
+    assert session.remaining == 2
+    assert session.next_card() == CardDto("aku", "mig", "ms", "da")
+
+
+def test_open_study_session_propagates_repository_error() -> None:
+    with pytest.raises(VocabularyNotFoundError):
+        open_study_session(_MissingRepository(), _first)

tests/unit/application/test_study_session.py

@@ -0,0 +1,60 @@
+"""Tests of the StudySession use case."""
+
+from collections.abc import Sequence
+
+from flash_card.application.dto.card_dto import CardDto
+from flash_card.application.use_cases.study_session import StudySession
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.deck import Deck
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+PAIR = LanguagePair("ms", "da")
+A = Card("aku", "mig")
+B = Card("kau", "du")
+
+
+def _first(cards: Sequence[Card]) -> Card:
+    return cards[0]
+
+
+def _session(*cards: Card) -> StudySession:
+    return StudySession(Deck(PAIR, cards), _first)
+
+
+def test_current_card_is_none_before_first_draw() -> None:
+    assert _session(A).current_card is None
+
+
+def test_next_card_returns_chosen_card_as_dto() -> None:
+    assert _session(A, B).next_card() == CardDto("aku", "mig", "ms", "da")
+
+
+def test_next_card_returns_different_card_when_two_or_more() -> None:
+    session = _session(A, B)
+    first = session.next_card()
+    second = session.next_card()
+    assert first != second
+    assert second == CardDto("kau", "du", "ms", "da")
+
+
+def test_next_card_returns_same_card_when_one() -> None:
+    session = _session(A)
+    assert session.next_card() == session.next_card()
+
+
+def test_next_card_returns_none_when_deck_is_empty() -> None:
+    session = _session()
+    assert session.next_card() is None
+    assert session.current_card is None
+
+
+def test_current_card_follows_last_draw() -> None:
+    session = _session(A, B)
+    shown = session.next_card()
+    assert session.current_card == shown
+
+
+def test_remaining_counts_cards_in_deck() -> None:
+    session = _session(A, B)
+    session.next_card()
+    assert session.remaining == 2

tests/unit/domain/test_card.py

@@ -0,0 +1,38 @@
+"""Tests of the Card, LanguagePair and Vocabulary value types."""
+
+import dataclasses
+
+import pytest
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.vocabulary import Vocabulary
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+
+def test_card_equals_card_with_same_texts() -> None:
+    assert Card("aku", "mig") == Card("aku", "mig")
+
+
+def test_card_is_frozen() -> None:
+    card = Card("aku", "mig")
+    with pytest.raises(dataclasses.FrozenInstanceError):
+        card.front = "kau"  # type: ignore[misc]
+
+
+def test_language_pair_holds_codes() -> None:
+    pair = LanguagePair("ms", "da")
+    assert (pair.front_code, pair.back_code) == ("ms", "da")
+
+
+def test_language_pair_is_frozen() -> None:
+    pair = LanguagePair("ms", "da")
+    with pytest.raises(dataclasses.FrozenInstanceError):
+        pair.front_code = "en"  # type: ignore[misc]
+
+
+def test_vocabulary_holds_pair_and_cards() -> None:
+    pair = LanguagePair("ms", "da")
+    cards = (Card("aku", "mig"),)
+    vocabulary = Vocabulary(pair, cards)
+    assert vocabulary.language_pair == pair
+    assert vocabulary.cards == cards

tests/unit/domain/test_deck.py

@@ -0,0 +1,73 @@
+"""Tests of the Deck entity."""
+
+from collections.abc import Sequence
+
+import pytest
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.deck import Deck
+from flash_card.domain.entities.vocabulary import Vocabulary
+from flash_card.domain.errors.vocabulary_errors import EmptyDeckError
+from flash_card.domain.value_objects.language_pair import LanguagePair
+
+PAIR = LanguagePair("ms", "da")
+A = Card("aku", "mig")
+B = Card("kau", "du")
+
+
+def _first(cards: Sequence[Card]) -> Card:
+    return cards[0]
+
+
+def test_from_vocabulary_holds_all_cards() -> None:
+    deck = Deck.from_vocabulary(Vocabulary(PAIR, (A, B)))
+    assert deck.cards == (A, B)
+    assert deck.language_pair == PAIR
+    assert len(deck) == 2
+
+
+def test_cards_returns_copy_when_deck_changes_later() -> None:
+    deck = Deck(PAIR, [A])
+    snapshot = deck.cards
+    deck.remove(A)
+    assert snapshot == (A,)
+    assert deck.is_empty
+
+
+def test_draw_returns_chosen_card() -> None:
+    assert Deck(PAIR, [A, B]).draw(_first) == A
+
+
+def test_draw_avoids_excluded_card_when_another_exists() -> None:
+    assert Deck(PAIR, [A, B]).draw(_first, exclude=A) == B
+
+
+def test_draw_returns_excluded_card_when_it_is_the_only_one() -> None:
+    assert Deck(PAIR, [A]).draw(_first, exclude=A) == A
+
+
+def test_draw_keeps_card_in_deck() -> None:
+    deck = Deck(PAIR, [A, B])
+    deck.draw(_first)
+    assert len(deck) == 2
+
+
+def test_draw_raises_when_deck_is_empty() -> None:
+    with pytest.raises(EmptyDeckError):
+        Deck(PAIR, []).draw(_first)
+
+
+def test_remove_deletes_first_equal_card() -> None:
+    deck = Deck(PAIR, [A, B, A])
+    deck.remove(A)
+    assert deck.cards == (B, A)
+
+
+def test_remove_raises_when_card_is_absent() -> None:
+    with pytest.raises(ValueError):
+        Deck(PAIR, [A]).remove(B)
+
+
+def test_is_empty_reflects_cards() -> None:
+    assert Deck(PAIR, []).is_empty
+    assert not Deck(PAIR, [A]).is_empty

tests/unit/domain/test_vocabulary_errors.py

@@ -0,0 +1,21 @@
+"""Tests of the vocabulary error hierarchy."""
+
+import pytest
+
+from flash_card.domain.errors.vocabulary_errors import (
+    EmptyDeckError,
+    VocabularyError,
+    VocabularyFormatError,
+    VocabularyNotFoundError,
+)
+
+
+@pytest.mark.parametrize(
+    "error", [VocabularyFormatError, VocabularyNotFoundError, EmptyDeckError]
+)
+def test_error_is_a_vocabulary_error(error: type[VocabularyError]) -> None:
+    assert issubclass(error, VocabularyError)
+
+
+def test_vocabulary_error_is_an_exception() -> None:
+    assert issubclass(VocabularyError, Exception)

tests/unit/infrastructure/test_csv_word_list.py

@@ -0,0 +1,95 @@
+"""Tests of read_word_list and CsvVocabularyRepository."""
+
+from pathlib import Path
+
+import pytest
+
+from flash_card.domain.entities.card import Card
+from flash_card.domain.errors.vocabulary_errors import (
+    VocabularyFormatError,
+    VocabularyNotFoundError,
+)
+from flash_card.domain.value_objects.language_pair import LanguagePair
+from flash_card.infrastructure.persistence.csv_vocabulary_repository import (
+    CsvVocabularyRepository,
+)
+from flash_card.infrastructure.persistence.csv_word_list import read_word_list
+
+
+def _write(path: Path, content: str) -> Path:
+    path.write_bytes(content.encode("utf-8"))
+    return path
+
+
+def test_read_word_list_returns_pair_and_cards(tmp_path: Path) -> None:
+    path = _write(tmp_path / "w.csv", "ms;da\naku;mig\nkau;du\n")
+    pair, cards = read_word_list(path)
+    assert pair == LanguagePair("ms", "da")
+    assert cards == (Card("aku", "mig"), Card("kau", "du"))
+
+
+def test_read_word_list_drops_byte_order_mark(tmp_path: Path) -> None:
+    path = _write(tmp_path / "w.csv", "ms;da\r\naku;mig\r\n")
+    pair, cards = read_word_list(path)
+    assert pair == LanguagePair("ms", "da")
+    assert cards == (Card("aku", "mig"),)
+
+
+def test_read_word_list_skips_blank_lines(tmp_path: Path) -> None:
+    path = _write(tmp_path / "w.csv", "\nms;da\n\naku;mig\n  \n;\nkau;du\n\n")
+    _pair, cards = read_word_list(path)
+    assert cards == (Card("aku", "mig"), Card("kau", "du"))
+
+
+def test_read_word_list_strips_whitespace(tmp_path: Path) -> None:
+    path = _write(tmp_path / "w.csv", " ms ; da \n aku ; mig \n")
+    pair, cards = read_word_list(path)
+    assert pair == LanguagePair("ms", "da")
+    assert cards == (Card("aku", "mig"),)
+
+
+def test_read_word_list_raises_not_found_when_file_is_missing(
+    tmp_path: Path,
+) -> None:
+    with pytest.raises(VocabularyNotFoundError) as info:
+        read_word_list(tmp_path / "missing.csv")
+    assert isinstance(info.value.__cause__, FileNotFoundError)
+
+
+def test_read_word_list_raises_format_error_when_file_is_empty(
+    tmp_path: Path,
+) -> None:
+    path = _write(tmp_path / "w.csv", "\n\n")
+    with pytest.raises(VocabularyFormatError, match="empty"):
+        read_word_list(path)
+
+
+@pytest.mark.parametrize("header", ["ms\n", "ms;da;en\n", "ms;\n"])
+def test_read_word_list_raises_format_error_for_bad_header(
+    tmp_path: Path, header: str
+) -> None:
+    path = _write(tmp_path / "w.csv", header + "aku;mig\n")
+    with pytest.raises(VocabularyFormatError, match="line 1"):
+        read_word_list(path)
+
+
+def test_read_word_list_raises_format_error_with_line_number_for_bad_row(
+    tmp_path: Path,
+) -> None:
+    path = _write(tmp_path / "w.csv", "ms;da\naku;mig\n\nkau;du;extra\n")
+    with pytest.raises(VocabularyFormatError, match="line 4") as info:
+        read_word_list(path)
+    assert str(path) in str(info.value)
+
+
+def test_repository_load_returns_vocabulary(tmp_path: Path) -> None:
+    path = _write(tmp_path / "w.csv", "ms;da\naku;mig\n")
+    vocabulary = CsvVocabularyRepository(path).load()
+    assert vocabulary.language_pair == LanguagePair("ms", "da")
+    assert vocabulary.cards == (Card("aku", "mig"),)
+
+
+def test_repository_load_raises_format_error_when_no_card(tmp_path: Path) -> None:
+    path = _write(tmp_path / "w.csv", "ms;da\n")
+    with pytest.raises(VocabularyFormatError):
+        CsvVocabularyRepository(path).load()

tests/unit/test_app.py

@@ -4,6 +4,8 @@
 @brief Checks main of flash_card.presentation.app without opening a window.
 """
 
+from pathlib import Path
+
 import pytest
 
 from flash_card.presentation import app
@@ -18,10 +20,24 @@ class _FakeRoot:
 
 
 def test_main_runs_main_loop_and_returns_zero(
-    monkeypatch: pytest.MonkeyPatch,
+    monkeypatch: pytest.MonkeyPatch, tmp_path: Path
 ) -> None:
     root = _FakeRoot()
-    monkeypatch.setattr(app, "create_application", lambda: (root, object()))
+    seen: list[Path | None] = []
 
-    assert app.main([]) == 0
+    def fake_create(data_dir: Path | None = None) -> tuple[_FakeRoot, object]:
+        seen.append(data_dir)
+        return root, object()
+
+    monkeypatch.setattr(app, "create_application", fake_create)
+
+    assert app.main(["--data-dir", str(tmp_path)]) == 0
     assert root.mainloop_calls == 1
+    assert seen == [tmp_path]
+
+
+def test_main_returns_one_when_word_list_is_missing(
+    tmp_path: Path, caplog: pytest.LogCaptureFixture
+) -> None:
+    assert app.main(["--data-dir", str(tmp_path / "nowhere")]) == 1
+    assert "word list not found" in caplog.text

tests/unit/test_constants.py

@@ -31,3 +31,7 @@ def test_language_names_cover_ms_and_da() -> None:
 
 def test_project_root_contains_pyproject() -> None:
     assert (constants.PROJECT_ROOT / "pyproject.toml").is_file()
+
+
+def test_csv_encoding_drops_byte_order_mark() -> None:
+    assert constants.CSV_ENCODING == "utf-8-sig"

tests/unit/test_flash_card_view_model.py

@@ -1,18 +1,53 @@
-"""Tests of the flash card view model.
+"""Tests of the flash card view model over a real session and in-memory deck."""
 
-@file test_flash_card_view_model.py
-@brief Checks the placeholder texts of FlashCardViewModel.
-"""
+from collections.abc import Sequence
 
-from flash_card.constants import PLACEHOLDER_LANGUAGE_NAME, PLACEHOLDER_WORD
+from flash_card.application.use_cases.study_session import StudySession
+from flash_card.constants import FINISHED_MESSAGE
+from flash_card.domain.entities.card import Card
+from flash_card.domain.entities.deck import Deck
+from flash_card.domain.value_objects.language_pair import LanguagePair
 from flash_card.presentation.features.flash_card.flash_card_view_model import (
     FlashCardViewModel,
 )
 
-
-def test_language_name_returns_placeholder() -> None:
-    assert FlashCardViewModel().language_name == PLACEHOLDER_LANGUAGE_NAME
+A = Card("aku", "mig")
+B = Card("kau", "du")
 
 
-def test_text_returns_placeholder_word() -> None:
-    assert FlashCardViewModel().text == PLACEHOLDER_WORD
+def _first(cards: Sequence[Card]) -> Card:
+    return cards[0]
+
+
+def _session(code: str, *cards: Card) -> StudySession:
+    return StudySession(Deck(LanguagePair(code, "da"), cards), _first)
+
+
+def test_view_model_draws_first_card_on_construction() -> None:
+    view_model = FlashCardViewModel(_session("ms", A, B))
+    assert view_model.text == "aku"
+    assert view_model.language_name == "Malay"
+    assert not view_model.is_finished
+
+
+def test_next_card_shows_next_card() -> None:
+    view_model = FlashCardViewModel(_session("ms", A, B))
+    view_model.next_card()
+    assert view_model.text == "kau"
+
+
+def test_language_name_shows_unknown_code_in_upper_case() -> None:
+    view_model = FlashCardViewModel(_session("xx", A))
+    assert view_model.language_name == "XX"
+
+
+def test_language_name_uses_given_names() -> None:
+    view_model = FlashCardViewModel(_session("ms", A), {"ms": "Melayu"})
+    assert view_model.language_name == "Melayu"
+
+
+def test_view_model_shows_finished_message_when_no_card_is_left() -> None:
+    view_model = FlashCardViewModel(_session("ms"))
+    assert view_model.is_finished
+    assert view_model.language_name == ""
+    assert view_model.text == FINISHED_MESSAGE