public void matchesSnapshot(BiConsumer<String, String> snapshotMatcher) {
      matchesSnapshot("", snapshotMatcher);
    }
Allows to specify a custom matcher for the snapshot.
<p>
This is useful when comparing json or similar, which have less strict equality rules.

@param snapshotMatcher a custom matcher for the snapshot, which is called with the snapshot value and the actual value.
                       The matcher must throw an {@link AssertionError} if the values don't match.
spock-core/src/main/java/spock/lang/Snapshotter.java