unittest/discover: Avoid adding test parent dir to sys.path.

When running tests from subfolders, import by "full dotted path" rather than
just module name, removing the need to add the test parent folder to sys.path.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

Author: andrewleech

python-stdlib/unittest-discover/tests/sub/sub.py

@@ -0,0 +1,2 @@
+# This is intended to be imported as 
+imported = True

python-stdlib/unittest-discover/tests/sub/test_module_import.py

@@ -0,0 +1,13 @@
+import sys
+import unittest
+
+
+class TestModuleImport(unittest.TestCase):
+    def test_ModuleImportPath(self):
+        try:
+            from sub.sub import imported
+            assert imported
+        except ImportError:
+            print("This test is intended to be run with unittest discover"
+                  "from the unittest-discover/tests dir. sys.path:", sys.path)
+            raise

python-stdlib/unittest-discover/unittest/__main__.py

@@ -6,19 +6,24 @@
 from fnmatch import fnmatch
 from micropython import const
 
-from unittest import TestRunner, TestResult, TestSuite
+try:
+    from unittest import TestRunner, TestResult, TestSuite
+except ImportError:
+    print("Error: This must be used from an installed copy of unittest-discover which will"
+          " also install base unittest module.")
+    raise
 
 
 # Run a single test in a clean environment.
 def _run_test_module(runner: TestRunner, module_name: str, *extra_paths: list[str]):
     module_snapshot = {k: v for k, v in sys.modules.items()}
     path_snapshot = sys.path[:]
     try:
-        for path in reversed(extra_paths):
+        for path in extra_paths:
             if path:
                 sys.path.insert(0, path)
 
-        module = __import__(module_name)
+        module = __import__(module_name, None, None, module_name)
         suite = TestSuite(module_name)
         suite._load_module(module)
         return runner.run(suite)
@@ -36,16 +41,18 @@ def _run_all_in_dir(runner: TestRunner, path: str, pattern: str, top: str):
     for fname, ftype, *_ in os.ilistdir(path):
         if fname in ("..", "."):
             continue
+        fpath = "/".join((path, fname))
         if ftype == _DIR_TYPE:
             result += _run_all_in_dir(
                 runner=runner,
-                path="/".join((path, fname)),
+                path=fpath,
                 pattern=pattern,
                 top=top,
             )
         if fnmatch(fname, pattern):
-            module_name = fname.rsplit(".", 1)[0]
-            result += _run_test_module(runner, module_name, path, top)
+            module_path = fpath.rsplit(".", 1)[0]  # remove ext
+            module_path = module_path.replace("/", ".").strip(".")
+            result += _run_test_module(runner, module_path, top)
     return result