Fix _compat tests (quantumlib#4926)

Fixes some of the out of order test breakage described in quantumlib#4921 

These tests are certainly broken, they are supposed to pass in the function not the result of the function.

Not sure I fully see why this interacts badly with test_deprecated_module tests, but once it hits one of these failing the following parameterized tests fail.

.github/workflows/ci.yml

@@ -314,7 +314,7 @@ jobs:
       - name: Install npm
         run: check/npm ci
       - name: Lint
-        run: check/ts-lint 
+        run: check/ts-lint
   ts-test:
     name: Typescript tests
     runs-on: ubuntu-20.04
@@ -325,7 +325,7 @@ jobs:
       - name: Install npm dependencies
         run: check/npm ci
       - name: Unit tests
-        run: check/ts-test 
+        run: check/ts-test
       - name: End to end tests
         run: check/ts-test-e2e
   ts-coverage:

cirq-core/cirq/_compat_test.py

@@ -598,6 +598,11 @@ def _trace_unhandled_exceptions(*args, queue: 'multiprocessing.Queue', func: Cal
 
 def subprocess_context(test_func):
     """Ensures that sys.modules changes in subprocesses won't impact the parent process."""
+    assert callable(test_func), (
+        "subprocess_context expects a function. Did you call the function instead of passing "
+        "it to this method?"
+    )
+
     import os
 
     ctx = multiprocessing.get_context('spawn' if os.name == 'nt' else 'fork')
@@ -609,8 +614,8 @@ def isolated_func(*args, **kwargs):
         kwargs['func'] = test_func
         p = ctx.Process(target=_trace_unhandled_exceptions, args=args, kwargs=kwargs)
         p.start()
-        result = exception.get()
         p.join()
+        result = exception.get()
         if result:
             # coverage: ignore
             ex_type, msg, ex_trace = result
@@ -667,8 +672,6 @@ def _test_deprecated_module_inner(outdated_method, deprecation_messages):
             deadline='v0.20',
             count=len(deprecation_messages),
         ):
-            import warnings
-
             warnings.simplefilter('always')
             outdated_method()
 
@@ -785,6 +788,7 @@ def _test_broken_module_1_inner():
 
 
 def _test_broken_module_2_inner():
+    warnings.simplefilter('always')
     with cirq.testing.assert_deprecated(deadline="v0.20", count=None):
         with pytest.raises(
             DeprecatedModuleImportError,
@@ -798,6 +802,9 @@ def _test_broken_module_2_inner():
 
 
 def _test_broken_module_3_inner():
+    import cirq.testing._compat_test_data
+
+    warnings.simplefilter('always')
     with cirq.testing.assert_deprecated(deadline="v0.20", count=None):
         with pytest.raises(
             DeprecatedModuleImportError,
@@ -807,15 +814,15 @@ def _test_broken_module_3_inner():
 
 
 def test_deprecated_module_error_handling_1():
-    subprocess_context(_test_broken_module_1_inner())
+    subprocess_context(_test_broken_module_1_inner)()
 
 
 def test_deprecated_module_error_handling_2():
-    subprocess_context(_test_broken_module_2_inner())
+    subprocess_context(_test_broken_module_2_inner)()
 
 
 def test_deprecated_module_error_handling_3():
-    subprocess_context(_test_broken_module_3_inner())
+    subprocess_context(_test_broken_module_3_inner)()
 
 
 def test_new_module_is_top_level():