test: add a test for skipping covered functions

tests/test_html.py

@@ -180,6 +180,8 @@ def run_coverage(
     def assert_htmlcov_files_exist(self) -> None:
         """Assert that all the expected htmlcov files exist."""
         self.assert_exists("htmlcov/index.html")
+        self.assert_exists("htmlcov/function_index.html")
+        self.assert_exists("htmlcov/class_index.html")
         self.assert_exists("htmlcov/main_file_py.html")
         self.assert_exists("htmlcov/helper1_py.html")
         self.assert_exists("htmlcov/helper2_py.html")
@@ -617,6 +619,26 @@ def normal():
         res = self.run_coverage(covargs=dict(source="."), htmlargs=dict(skip_covered=True))
         assert res == 100.0
         self.assert_doesnt_exist("htmlcov/main_file_py.html")
+        # Since there are no files to report, we can't collect any region
+        # information, so there are no region-based index pages.
+        self.assert_doesnt_exist("htmlcov/function_index.html")
+        self.assert_doesnt_exist("htmlcov/class_index.html")
+
+    def test_report_skip_covered_100_functions(self) -> None:
+        self.make_file("main_file.py", """\
+            def normal():
+                print("z")
+            def abnormal():
+                print("a")
+            normal()
+        """)
+        res = self.run_coverage(covargs=dict(source="."), htmlargs=dict(skip_covered=True))
+        assert res == 80.0
+        self.assert_exists("htmlcov/main_file_py.html")
+        # We have a file to report, so we get function and class index pages,
+        # even though there are no classes.
+        self.assert_exists("htmlcov/function_index.html")
+        self.assert_exists("htmlcov/class_index.html")
 
     def make_init_and_main(self) -> None:
         """Helper to create files for skip_empty scenarios."""