Spring Cannot assert status reason phrase with MockMvcTester

When using MockMvc the status reason phrase can be asserted like this:

mockMvc
    .perform(get("/something"))
    .andExpect(status().isNotFound())
    .andExpect(status().reason("Could not find xyz"))

This cannot be achieved using MockMvcTester:

val result = mockMvc.get().uri("/something")
assertThat(result)
    .hasStatus(HttpStatus.NOT_FOUND)
    // ??? How to assert the status reason phrase

Is there something I'm missing?

Comment From: snicoll

Thanks for the report. I don't think you're missing anything, except the reason bit is a bit misleading. It's actually the error message that's available only when HttpServletResponse#sendError(int, String) is called.

We don't offer a direct assertion for that and we need to figure out if we want. In the meantime you can use the following:

assertThat(result.getResponse().getErrorMessage()).isEqualTo("Could not find xyz");

Comment From: bclozel

I went ahead and added a mvc.get().uri("/user/42")).hasErrorMessage("error message") assertion for this. This is not a common use case, but servletResponse.sendError(int, String) is still called by Spring Framework in some features like @ResponseStatus(code = HttpStatus.BAD_REQUEST, reason = "my error message"). While it's referred as "status reason" in this case, this message is not sent on the HTTP response status line but is rather a Servlet error message dedicated to Servlet error pages. I believe hasErrorMessage and the companion Javadoc fits that description.