Allowed methods are not respected in unit tests

class BookController {

    static allowedMethods = [index: "POST"]

    def index() {
        println "Method is ${request.method}"
        redirect(action: "ok")
    }

    def ok () {
        render(view: "ok")
    }
}

@TestFor(BookController)
class BookControllerTests {

    void testMethodGet() {
        request.method = "GET"
        controller.index()
        println("In test, request redirectUrl is ${response.redirectUrl} and it should be null")
        assert response.status == HttpServletResponse.SC_METHOD_NOT_ALLOWED
        assert response.redirectUrl == null
    }

    void testMethodPost() {
        request.method = "POST"
        controller.index()
        assert response.redirectUrl == "/book/ok"
    }
}

Method is GET
In test, request redirectUrl is /book/ok and it should be null
| Failure:  testMethodGet(rc3methodnotallowed.BookControllerTests)
|  Assertion failed: 

assert response.status == HttpServletResponse.SC_METHOD_NOT_ALLOWED
       |        |      |                      |
       |        302    false                  405
       org.codehaus.groovy.grails.plugins.testing.GrailsMockHttpServletResponse@1b030d8

	at rc3methodnotallowed.BookControllerTests.testMethodGet(BookControllerTests.groovy:16)