Package is is a mini testing helper. is.OK asserts that the specified object is OK, which means different things for different types: is.Equal asserts that two objects are effectively equal. is.Panic and is.PanicWith asserts that the func() will panic. PanicWith specifies the panic text that is expected: To prevent is from stopping when the first assertion fails, you can use is.Relaxed(t), rather than is.New(t).