tests: Add termination tests for Dummy provider

Add termination tests for the Dummy provider, so that we can have
cross-platform coverage in our Windows/macOS CI runners, which can't use
the Container isolation providers.

tests/isolation_provider/test_dummy.py

@@ -0,0 +1,53 @@
+import os
+import subprocess
+
+import pytest
+from pytest_mock import MockerFixture
+
+from dangerzone.conversion import errors
+from dangerzone.document import Document
+from dangerzone.isolation_provider.base import IsolationProvider
+from dangerzone.isolation_provider.dummy import Dummy
+
+from .base import IsolationProviderTermination, IsolationProviderTest
+
+
+class DummyWait(Dummy):
+    """Dummy isolation provider that spawns a blocking process."""
+
+    def start_doc_to_pixels_proc(self, document: Document) -> subprocess.Popen:
+        return subprocess.Popen(
+            ["python3"],
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        )
+
+    def terminate_doc_to_pixels_proc(
+        self, document: Document, p: subprocess.Popen
+    ) -> None:
+        p.terminate()
+
+
+@pytest.fixture
+def provider_wait() -> DummyWait:
+    return DummyWait()
+
+
+@pytest.mark.skipif(
+    os.environ.get("DUMMY_CONVERSION", False) == False,
+    reason="can only run for dummy conversions",
+)
+class TestDummyTermination(IsolationProviderTermination):
+
+    def test_failed(
+        self,
+        provider_wait: IsolationProvider,
+        mocker: MockerFixture,
+    ) -> None:
+        mocker.patch.object(
+            provider_wait,
+            "get_proc_exception",
+            return_value=errors.DocFormatUnsupported(),
+        )
+        super().test_failed(provider_wait, mocker)