Add the tests for create, export and the main flow

Task: MIL-004#4

tests/test_export.py

@@ -0,0 +1,52 @@
+"""Tests of the creation and the export of the scores table."""
+
+from pathlib import Path
+
+import pytest
+
+pandas = pytest.importorskip("pandas")
+
+from weather import export  # noqa: E402
+
+
+def test_create_scores_frame_has_the_columns_and_values_of_the_lecture() -> None:
+    frame = export.create_scores_frame()
+
+    assert isinstance(frame, pandas.DataFrame)
+    assert list(frame.columns) == ["students", "scores"]
+    assert frame["students"].to_list() == ["Amy", "James", "Angela"]
+    assert frame["scores"].to_list() == [76, 56, 65]
+
+
+def test_export_frame_round_trips_through_a_file(tmp_path: Path) -> None:
+    frame = export.create_scores_frame()
+    target = tmp_path / "scores.csv"
+
+    export.export_frame(frame, target)
+
+    assert target.is_file()
+    read_back = pandas.read_csv(target, index_col=0)
+    pandas.testing.assert_frame_equal(read_back, frame)
+
+
+def test_export_frame_accepts_a_string_path(tmp_path: Path) -> None:
+    target = tmp_path / "as_text.csv"
+
+    export.export_frame(export.create_scores_frame(), str(target))
+
+    assert target.is_file()
+
+
+def test_export_frame_default_name_writes_only_new_data_csv_in_the_working_dir(
+    tmp_path: Path,
+) -> None:
+    # The autouse fixture in conftest.py made tmp_path the working directory.
+    export.export_frame(export.create_scores_frame())
+
+    assert [item.name for item in tmp_path.iterdir()] == ["new_data.csv"]
+
+
+def test_create_scores_frame_writes_nothing(tmp_path: Path) -> None:
+    export.create_scores_frame()
+
+    assert list(tmp_path.iterdir()) == []