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`.

This matches CPython more closely, which places `abspath(top)` at the start
of `sys.path` but doesn't include the test file parent dir at all.

It fixes issues where projects may include a `test_xxx.py` file in their
distribution which would (prior to this change) be unintentionally found by
unittest-discover.

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

python-stdlib/unittest-discover/manifest.py

@@ -1,4 +1,4 @@
-metadata(version="0.1.2")
+metadata(version="0.1.3")
 
 require("argparse")
 require("fnmatch")

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

@@ -0,0 +1 @@
+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

@@ -6,7 +6,12 @@ import sys
 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.
@@ -14,11 +19,11 @@ def _run_test_module(runner: TestRunner, module_name: str, *extra_paths: list[st
     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