fix(ci-insights): Disable flaky detection without existing tests (#239)

Fixes: MRGFY-5913

Author: remyduthu

pytest_mergify/flaky_detection.py

@@ -65,7 +65,13 @@ def _fetch_existing_tests(self) -> typing.List[str]:
 
         response.raise_for_status()
 
-        return typing.cast(typing.List[str], response.json()["test_names"])
+        result = typing.cast(typing.List[str], response.json()["test_names"])
+        if len(result) == 0:
+            raise RuntimeError(
+                f"No existing tests found for '{self.full_repository_name}' repository on branch '{self.branch_name}'",
+            )
+
+        return result
 
     def detect_from_report(self, report: _pytest.reports.TestReport) -> bool:
         if report.when != "call":

tests/test_ci_insights.py

@@ -72,6 +72,24 @@ def test_load_flaky_detection_error(monkeypatch: pytest.MonkeyPatch) -> None:
     assert "500 Server Error" in client.flaky_detector_error_message
 
 
+@responses.activate
+def test_load_flaky_detection_error_without_existing_tests(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    _set_test_environment(monkeypatch)
+
+    _make_quarantine_mock()
+    _make_test_names_mock([])
+
+    client = _make_test_client()
+    assert client.flaky_detector is None
+    assert client.flaky_detector_error_message is not None
+    assert (
+        "No existing tests found for 'Mergifyio/pytest-mergify' repository on branch 'main'"
+        in client.flaky_detector_error_message
+    )
+
+
 @responses.activate
 def test_flaky_detection(
     monkeypatch: pytest.MonkeyPatch,