Add more explicit comments to pyptoject tests

Author: amol-

tests/test_pyproject.py

@@ -8,6 +8,12 @@
 HERE = os.path.dirname(__file__)
 PROJECTS_DIRECTORY = os.path.abspath(os.path.join(HERE, "testdata", "python-project"))
 
+# Most of this tests, verify against three fixture projects that are located in PROJECTS_DIRECTORY
+# - using_pyproject: contains a pyproject.toml file with a project.requires-python field
+# - using_setupcfg: contains a setup.cfg file with a options.python_requires field
+# - using_pyversion: contains a .python-version file and a pyproject.toml file without any version constraint.
+# - allofthem: contains all metadata files all with different version constraints.
+
 
 @pytest.mark.parametrize(
     "project_dir, expected",
@@ -26,6 +32,7 @@
     ids=["pyproject.toml", "setup.cfg", ".python-version", "allofthem"],
 )
 def test_python_project_metadata_detect(project_dir, expected):
+    """Test that the metadata files are detected when they exist."""
     expectation = [(f, pathlib.Path(project_dir) / f) for f in expected]
     assert lookup_metadata_file(project_dir) == expectation
 
@@ -39,6 +46,7 @@ def test_python_project_metadata_detect(project_dir, expected):
     ids=["empty", "missing"],
 )
 def test_python_project_metadata_missing(project_dir):
+    """Test that lookup_metadata_file is able to deal with missing or empty directories."""
     assert lookup_metadata_file(project_dir) == []
 
 
@@ -51,5 +59,9 @@ def test_python_project_metadata_missing(project_dir):
     ids=["option-exists", "option-missing"],
 )
 def test_pyprojecttoml_python_requires(project_dir, expected):
+    """Test that the python_requires field is correctly parsed from pyproject.toml.
+
+    Both when the option exists or when it missing in the pyproject.toml file.
+    """
     pyproject_file = pathlib.Path(project_dir) / "pyproject.toml"
     assert parse_pyproject_python_requires(pyproject_file) == expected