Implemented acceptance test TestIsoScope.test_single_scope_subset_of_workers_utilized.

Author: vkruglik-aka

testing/acceptance_test.py

@@ -1285,6 +1285,29 @@ def test(i):
         assert counts_by_worker["gw1"] in (2, 3)
         assert counts_by_worker["gw0"] + counts_by_worker["gw1"] == 5
 
+    @pytest.mark.parametrize('num_tests', [1, 2, 3])
+    def test_single_scope_subset_of_workers_utilized(self,
+                                                     num_tests: int,
+                                                     pytester: pytest.Pytester) -> None:
+        """
+        With single scope, there are no fence tests from another scope, so
+        this scheduler resorts to shutting down the workers in order to execute
+        the final tests in each worker. isoscope allocates at least two tests
+        per worker from the active scope, unless the scope has only one test.
+        """
+        test_file = f"""
+            import pytest
+            @pytest.mark.parametrize('i', range({num_tests}))
+            def test(i):
+                pass
+        """
+        pytester.makepyfile(test_a=test_file)
+        result = pytester.runpytest("-n2", "--dist=isoscope", "-v")
+        counts_by_worker = get_workers_and_test_count_by_prefix("test_a.py::test", result.outlines)
+        assert counts_by_worker["gw0"] in (0, num_tests)
+        assert counts_by_worker["gw1"] in (0, num_tests)
+        assert counts_by_worker["gw0"] + counts_by_worker["gw1"] == num_tests
+
 
 class TestLoadScope:
     def test_by_module(self, pytester: pytest.Pytester) -> None: