fix: show snapshot data in report when does not exist (#191)

* fix: show snapshot data in report when does not exist

* test: unsaved snapshot gets printed out

src/syrupy/assertion.py

@@ -72,7 +72,7 @@ def executions(self) -> Dict[int, AssertionResult]:
         return self._execution_results
 
     def use_extension(
-        self, extension_class: Optional[Type["AbstractSyrupyExtension"]] = None,
+        self, extension_class: Optional[Type["AbstractSyrupyExtension"]] = None
     ) -> "SnapshotAssertion":
         """
         Creates a new snapshot assertion fixture with the same options but using
@@ -92,12 +92,11 @@ def get_assert_diff(self, data: "SerializableData") -> List[str]:
         assertion_result = self._execution_results[self.num_executions - 1]
         snapshot_data = assertion_result.recalled_data
         serialized_data = self.extension.serialize(data)
-        if snapshot_data is None:
-            return [gettext("Snapshot does not exist!")]
-
         diff: List[str] = []
+        if snapshot_data is None:
+            diff.append(gettext("Snapshot does not exist!"))
         if not assertion_result.success:
-            diff.extend(self.extension.diff_lines(serialized_data, snapshot_data))
+            diff.extend(self.extension.diff_lines(serialized_data, snapshot_data or ""))
         return diff
 
     def __call__(

tests/test_integration_single_file.py

@@ -64,10 +64,12 @@ def test_passed_single(snapshot_single):
     return {**testcases, **updated_testcases}
 
 
-def test_unsaved_snapshots(testdir, testcases):
+def test_unsaved_snapshots(snapshot, testdir, testcases):
     testdir.makepyfile(test_file=testcases["passed"])
     result = testdir.runpytest("-v")
-    assert "Snapshot does not exist" in clean_output(result.stdout.str())
+    output = clean_output(result.stdout.str())
+    assert "Snapshot does not exist" in output
+    assert "+ b'passed1'" in output
     assert result.ret == 1