refactor test_main_format_cells(), run pytest-cov in CI

Author: janosh

.github/workflows/test.yml

@@ -24,4 +24,4 @@ jobs:
         run: pip install .[test]
 
       - name: Run tests
-        run: pytest
+        run: pytest --cov format_ipy_cells

format_ipy_cells/main.py

@@ -59,9 +59,9 @@ def main(argv: Sequence[str] = []) -> int:
     """
     parser = ArgumentParser()
 
-    fic_version = md.version(pkg_name := "format-ipy-cells")
+    pkg_version = md.version(pkg_name := "format-ipy-cells")
     parser.add_argument(
-        "-v", "--version", action="version", version=f"{pkg_name} v{fic_version}"
+        "-v", "--version", action="version", version=f"{pkg_name} v{pkg_version}"
     )
 
     parser.add_argument("filenames", nargs="*", help="Filenames to format")

setup.cfg

@@ -31,7 +31,7 @@ console_scripts =
 
 [options.extras_require]
 # Used during pip install .[test]
-test = pytest
+test = pytest; pytest-cov
 
 [tool:pytest]
 testpaths = tests

tests/test_main.py

@@ -1,31 +1,33 @@
+import filecmp
 from importlib.metadata import version
+from shutil import copy2
 
 import pytest
 
 from format_ipy_cells.main import main
 
 
 def test_main_format_cells(capsys, tmpdir):
+    clean_nb = "tests/fixtures/clean_nb.py"
 
-    with open("tests/fixtures/raw_nb.py") as file:
-        raw_txt = file.read()
+    raw_file = copy2("tests/fixtures/raw_nb.py", tmpdir)
+    # test we leave clean file as is and don't write logs about it
+    clean_file = copy2(clean_nb, tmpdir)
 
-    with open("tests/fixtures/clean_nb.py") as file:
-        clean_txt = file.read()
-
-    # empty file to test we don't modify files needlessly
-    file1 = tmpdir.join("file1.py").ensure()
-
-    file2 = tmpdir.join("file2.py")
-    file2.write(raw_txt)
-
-    ret = main((str(file1), str(file2)))
+    ret = main((raw_file, clean_file))
 
     assert ret == 1
-    assert file2.read() == clean_txt
+    assert filecmp.cmp(raw_file, clean_nb), "Formatted file has unexpected content"
+    assert filecmp.cmp(clean_file, clean_nb), "clean file should not have changed"
+
+    out, err = capsys.readouterr()
+    assert out == f"Rewriting {raw_file}\n"
+    assert err == ""
 
-    out, _ = capsys.readouterr()
-    assert out == f"Rewriting {file2}\n"
+    ret = main([clean_file])
+    assert ret == 0, "expected exit code 0 when no files were changed"
+    out, err = capsys.readouterr()
+    assert out == err == ""
 
 
 def test_main_print_version(capsys):