# Wildcard vs. Fixture Refactor: Asserting Evolving API Schemas in Karate

Direct answer

Yes. Using the # wildcard in a Karate match lets the test ignore extra or missing fields, so a newly added field (even if it becomes required by the API) will not cause the test to fail. The test will still fail if a field is removed, its type changes, or a required field you explicitly asserted is missing.

When to refactor fixtures with call/callonce

Refactor when:

• The same expected payload (or a large part of it) appears in three or more test files.
• Schema changes happen frequently and you want a single place to update the fixture.
• You need to assert specific required fields and cannot rely on # tolerance.

Keep wildcard tolerance when:

• Only a few tests use the schema and the payload is small.
• The API is known to add optional fields that you intentionally want to ignore.
• You are validating a contract where extra fields are harmless and you prefer low maintenance.

Impact of Karate version on wildcard reliability

Karate 0.9.6+ introduced recursive # matching, meaning # works at any depth in nested JSON without needing explicit path wildcards. In versions prior to 0.9.6, # only matched at the literal position you wrote it; nested structures required you to repeat # at each level or use a custom predicate, making complex assertions less reliable and more verbose. Therefore, if you are on Karate 0.9.6 or later, you can safely use # deep inside objects and arrays and expect the same tolerance behavior. On older versions, verify that the wildcard behaves as expected by checking the rendered match expression.

Verification steps

1. Check the Karate version in use:

   * def karateVersion = karate.version

   and ensure it is >= 0.9.6 for recursive behavior.
2. Create a small test that matches a nested JSON with # at multiple levels, run it against a known‑good response and against a response where a new required field is added; observe that the test passes in both cases (showing the masking effect).
3. Refactor a duplicated match block into a callonce fixture, update the fixture once, and re‑run all referencing tests to confirm they still pass.