Add support for --pdb in subtests

Fix pytest-dev#22

CHANGELOG.rst

@@ -1,6 +1,13 @@
 CHANGELOG
 =========
 
+0.4.0 (2020-12-13)
+------------------
+
+* Add support for ``--pdb`` (`#22`_).
+
+.. _#22: https://github.com/pytest-dev/pytest-subtests/issues/22
+
 0.3.2 (2020-08-01)
 ------------------
 

pytest_subtests.py

@@ -11,6 +11,7 @@
 from _pytest.outcomes import OutcomeException
 from _pytest.reports import TestReport
 from _pytest.runner import CallInfo
+from _pytest.runner import check_interactive_exception
 from _pytest.unittest import TestCaseFunction
 
 if sys.version_info[:2] < (3, 7):
@@ -80,6 +81,10 @@ def _addSubTest(self, test_case, test, exc_info):
         sub_report = SubTestReport.from_item_and_call(item=self, call=call_info)
         sub_report.context = SubTestContext(msg, dict(test.params))
         self.ihook.pytest_runtest_logreport(report=sub_report)
+        if check_interactive_exception(call_info, sub_report):
+            self.ihook.pytest_exception_interact(
+                node=self, call=call_info, report=sub_report
+            )
 
 
 def pytest_configure(config):
@@ -174,6 +179,11 @@ def test(self, msg=None, **kwargs):
         with self.suspend_capture_ctx():
             self.ihook.pytest_runtest_logreport(report=sub_report)
 
+        if check_interactive_exception(call_info, sub_report):
+            self.ihook.pytest_exception_interact(
+                node=self.item, call=call_info, report=sub_report
+            )
+
 
 def make_call_info(exc_info, *, start, stop, duration, when):
     try:

tests/test_subtests.py

@@ -307,3 +307,63 @@ def test(subtests, {fixture}):
         result.stdout.fnmatch_lines(
             ["*1 passed*",]
         )
+
+
+class TestDebugging:
+    """Check --pdb support for subtests fixture and TestCase.subTest."""
+
+    class _FakePdb:
+        """
+        Fake debugger class implementation that tracks which methods were called on it.
+        """
+
+        quitting = False
+        calls = []
+
+        def __init__(self, *args, **kwargs):
+            self.calls.append("init")
+
+        def reset(self):
+            self.calls.append("reset")
+
+        def interaction(self, *args):
+            self.calls.append("interaction")
+
+    @pytest.fixture(autouse=True)
+    def cleanup_calls(self):
+        self._FakePdb.calls.clear()
+
+    def test_pdb_fixture(self, testdir, monkeypatch):
+        testdir.makepyfile(
+            """
+            def test(subtests):
+                with subtests.test():
+                    assert 0
+            """
+        )
+        self.runpytest_and_check_pdb(testdir, monkeypatch)
+
+    def test_pdb_unittest(self, testdir, monkeypatch):
+        testdir.makepyfile(
+            """
+            from unittest import TestCase
+            class Test(TestCase):
+                def test(self):
+                    with self.subTest():
+                        assert 0
+            """
+        )
+        self.runpytest_and_check_pdb(testdir, monkeypatch)
+
+    def runpytest_and_check_pdb(self, testdir, monkeypatch):
+        # Install the fake pdb implementation in pytest_subtests so we can reference
+        # it in the command line (any module would do).
+        import pytest_subtests
+
+        monkeypatch.setattr(pytest_subtests, "_CustomPdb", self._FakePdb, raising=False)
+        result = testdir.runpytest("--pdb", "--pdbcls=pytest_subtests:_CustomPdb")
+
+        # Ensure pytest entered in debugging mode when encountering the failing
+        # assert.
+        result.stdout.fnmatch_lines("*entering PDB*")
+        assert self._FakePdb.calls == ["init", "reset", "interaction"]