Add the tests for the csv reader

Task: MIL-002#4

tests/test_csv_reader.py

@@ -0,0 +1,77 @@
+"""Tests of the csv reader against the real data file and small files."""
+
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+
+from weather import csv_reader
+from weather.constants import DATA_FILE
+
+LECTURE_TEMPERATURES = [12, 14, 15, 14, 21, 22, 24]
+
+
+@pytest.fixture
+def small_csv(tmp_path: Path) -> Path:
+    file = tmp_path / "small.csv"
+    file.write_text("day,temp,condition\nMonday,3,Rain\nTuesday,-4,Snow\n")
+    return file
+
+
+def test_read_rows_gives_header_first_and_eight_rows_for_the_real_file() -> None:
+    rows = csv_reader.read_rows()
+
+    assert rows[0] == ["day", "temp", "condition"]
+    assert len(rows) == 8
+    assert all(isinstance(value, str) for row in rows for value in row)
+
+
+def test_read_temperatures_gives_the_lecture_values_for_the_real_file() -> None:
+    temperatures = csv_reader.read_temperatures()
+
+    assert temperatures == LECTURE_TEMPERATURES
+    assert all(isinstance(value, int) for value in temperatures)
+
+
+def test_read_temperatures_skips_the_header() -> None:
+    assert len(csv_reader.read_temperatures()) == len(csv_reader.read_rows()) - 1
+
+
+def test_read_temperatures_gives_the_values_of_a_small_file(small_csv: Path) -> None:
+    assert csv_reader.read_temperatures(small_csv) == [3, -4]
+
+
+def test_read_rows_gives_the_rows_of_a_small_file(small_csv: Path) -> None:
+    assert csv_reader.read_rows(small_csv) == [
+        ["day", "temp", "condition"],
+        ["Monday", "3", "Rain"],
+        ["Tuesday", "-4", "Snow"],
+    ]
+
+
+def test_default_path_works_from_another_working_directory(tmp_path: Path) -> None:
+    assert Path.cwd() == tmp_path
+    assert DATA_FILE.parent != Path.cwd()
+
+    assert csv_reader.read_temperatures() == LECTURE_TEMPERATURES
+
+
+def test_path_argument_overrides_the_default_as_str_and_as_path(
+    small_csv: Path,
+) -> None:
+    assert csv_reader.read_temperatures(small_csv) == [3, -4]
+    assert csv_reader.read_temperatures(str(small_csv)) == [3, -4]
+
+
+def test_importing_csv_reader_does_not_import_pandas() -> None:
+    code = "import sys, weather.csv_reader; sys.exit('pandas' in sys.modules)"
+
+    result = subprocess.run(
+        [sys.executable, "-I", "-c", code],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+    assert result.returncode == 0, result.stderr