unittest: Add exception capturing for subTest.

python-stdlib/unittest/test_unittest.py

@@ -148,6 +148,14 @@ class TestUnittestAssertions(unittest.TestCase):
         assert global_context is None
         global_context = True
 
+    def test_subtest_even(self):
+        """
+        Test that numbers between 0 and 5 are all even.
+        """
+        for i in range(0, 10, 2):
+            with self.subTest("Should only pass for even numbers", i=i):
+                self.assertEqual(i % 2, 0)
+
 
 if __name__ == "__main__":
     unittest.main()

python-stdlib/unittest/unittest.py

@@ -37,11 +37,35 @@ class AssertRaisesContext:
         return False
 
 
+# These are used to provide required context to things like subTest
+__current_test__ = None
+__test_result__ = None
+
+
+class SubtestContext:
+    def __enter__(self):
+        pass
+
+    def __exit__(self, *exc_info):
+        if exc_info[0] is not None:
+            # Exception raised
+            global __test_result__, __current_test__
+            handle_test_exception(
+                __current_test__,
+                __test_result__,
+                exc_info
+            )
+        # Suppress the exception as we've captured it above
+        return True
+
+
+
+
 class NullContext:
     def __enter__(self):
         pass
 
-    def __exit__(self, a, b, c):
+    def __exit__(self, exc_type, exc_value, traceback):
         pass
 
 
@@ -61,7 +85,7 @@ class TestCase:
                 func(*args, **kwargs)
 
     def subTest(self, msg=None, **params):
-        return NullContext()
+        return SubtestContext(msg=msg, params=params)
 
     def skipTest(self, reason):
         raise SkipTest(reason)
@@ -298,15 +322,29 @@ class TestResult:
         return self
 
 
-def capture_exc(e):
+def capture_exc(exc, traceback):
     buf = io.StringIO()
     if hasattr(sys, "print_exception"):
-        sys.print_exception(e, buf)
+        sys.print_exception(exc, buf)
     elif traceback is not None:
-        traceback.print_exception(None, e, sys.exc_info()[2], file=buf)
+        traceback.print_exception(None, exc, traceback, file=buf)
     return buf.getvalue()
 
 
+def handle_test_exception(current_test: tuple, test_result: TestResult, exc_info: tuple):
+    exc = exc_info[1]
+    traceback =  exc_info[2]
+    ex_str = capture_exc(exc, traceback)
+    if isinstance(exc, AssertionError):
+        test_result.failuresNum += 1
+        test_result.failures.append((current_test, ex_str))
+        print(" FAIL")
+    else:
+        test_result.errorsNum += 1
+        test_result.errors.append((current_test, ex_str))
+        print(" ERROR")
+
+
 def run_suite(c, test_result, suite_name=""):
     if isinstance(c, TestSuite):
         c.run(test_result)
@@ -324,29 +362,34 @@ def run_suite(c, test_result, suite_name=""):
     except AttributeError:
         pass
 
-    def run_one(m):
+    def run_one(test_function):
+        global __test_result__, __current_test__
         print("%s (%s) ..." % (name, suite_name), end="")
         set_up()
+        __test_result__ = test_result
+        test_container = f"({suite_name})"
+        __current_test__ = (name, test_container)
         try:
             test_result.testsRun += 1
-            m()
+            test_globals = dict(**globals())
+            test_globals["test_function"] = test_function
+            exec("test_function()", test_globals, test_globals)
+            # No exception occurred, test passed
             print(" ok")
         except SkipTest as e:
             print(" skipped:", e.args[0])
             test_result.skippedNum += 1
         except Exception as ex:
-            ex_str = capture_exc(ex)
-            if isinstance(ex, AssertionError):
-                test_result.failuresNum += 1
-                test_result.failures.append(((name, c), ex_str))
-                print(" FAIL")
-            else:
-                test_result.errorsNum += 1
-                test_result.errors.append(((name, c), ex_str))
-                print(" ERROR")
+            handle_test_exception(
+                current_test=(name, c),
+                test_result=test_result,
+                exc_info=sys.exc_info()
+            )
             # Uncomment to investigate failure in detail
             # raise
         finally:
+            __test_result__ = None
+            __current_test__ = None
             tear_down()
             try:
                 o.doCleanups()