fix: report usage of unknown inline-snapshot flags

src/inline_snapshot/pytest_plugin.py

@@ -66,6 +66,12 @@ def pytest_configure(config):
                 f"--inline-snapshot={','.join(flags)} can not be combined with xdist"
             )
 
+    unknown_flags = flags - categories - {"disable", "review", "report", "short-report"}
+    if unknown_flags:
+        raise pytest.UsageError(
+            f"--inline-snapshot={','.join(sorted(unknown_flags))} is a unknown flag"
+        )
+
     if "disable" in flags and flags != {"disable"}:
         raise pytest.UsageError(
             f"--inline-snapshot=disable can not be combined with other flags ({', '.join(flags-{'disable'})})"

src/inline_snapshot/testing/_example.py

@@ -209,6 +209,7 @@ def run_pytest(
         env: dict[str, str] = {},
         changed_files: Snapshot[dict[str, str]] | None = None,
         report: Snapshot[str] | None = None,
+        stderr: Snapshot[str] | None = None,
         returncode: Snapshot[int] | None = None,
     ) -> Example:
         """Run pytest with the given args and env variables in an seperate
@@ -255,6 +256,9 @@ def run_pytest(
             if returncode is not None:
                 assert result.returncode == returncode
 
+            if stderr is not None:
+                assert result.stderr.decode() == stderr
+
             if report is not None:
 
                 report_list = []

tests/test_pytest_plugin.py

@@ -628,3 +628,23 @@ def test_a():
 """
         ),
     )
+
+
+def test_unknown_flag():
+
+    Example(
+        """\
+def test_a():
+    assert 1==1
+"""
+    ).run_pytest(
+        ["--inline-snapshot=creaigflen"],
+        report=snapshot(""),
+        returncode=snapshot(4),
+        stderr=snapshot(
+            """\
+ERROR: --inline-snapshot=creaigflen is a unknown flag
+
+"""
+        ),
+    )