Check stepMismatch results for type=month. On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". Empty values PASS stepMismatchFor("", null, null) is false PASS stepMismatchFor("", "2", "1969-12") is false Normal step values PASS stepMismatchFor("2010-03", "2", "2010-02") is true PASS stepMismatchFor("2010-02", "2", "2010-02") is false PASS stepMismatchFor("2010-04", "2", "2010-02") is false PASS stepMismatchFor("1800-11", "3", "1800-09") is true PASS stepMismatchFor("1800-09", "3", "1800-09") is false PASS stepMismatchFor("1800-12", "3", "1800-09") is false PASS stepMismatchFor("275760-09", "3", "275760-08") is true PASS stepMismatchFor("275760-09", "2", "275760-09") is false Implicit step base PASS stepMismatchFor("1970-02", "2", null) is true PASS stepMismatchFor("1970-03", "2", null) is false Fractional step values PASS stepMismatchFor("2010-03", "0.1", "2010-02") is false PASS stepMismatchFor("2010-03", "1.1", "2010-02") is false PASS stepMismatchFor("2010-03", "1.9", "2010-02") is true Invalid or no step values PASS stepMismatchFor("2010-03", null, "2010-02") is false PASS stepMismatchFor("2010-03", "-1", "2010-02") is false PASS stepMismatchFor("2010-03", "foo", "2010-02") is false Special step value PASS stepMismatchFor("2010-03", "any", "2010-02") is false Disabled PASS stepMismatchFor("2010-03", "2", "2010-02", true) is true PASS successfullyParsed is true TEST COMPLETE