Even though SERVER-96944 introduces JSON output format to assert functions, however, many assert invocations add objects to the message, e.g.:

assert.eq(1, docs.length, "unexpected number of documents : " + tojson(docs));

This would serialize 'docs' into a string, which is undesirable. A better alternative:

assert.eq(1, docs.length, "unexpected number of documents", {docs});