How to call call request.JSON multiple times in Grails unit tests? - unit-testing

Question

I am upgrading my application from Grails 2.5.6 to Grails 4.0.3. Now I have lots of unit tests failed because I am calling controller methods with request.JSON multiple times in a single test. Those unit tests worked fine in old Grails 2.5.6.
To demonstrate the problem, I have a controller with the following method:
class TestController {
def testJson(){
def json = request.JSON
render(contentType:'application/json', text:json.toString(), encoding: "UTF-8")
}
}
And I have a unit test like this:
class TestControllerSpec extends Specification implements ControllerUnitTest<TestController> {
void "test json"(){
when:
request.json = [
a:1, b:2, c:3
]
controller.testJson()
then:
response.json.a == 1
response.json.b == 2
response.json.c == 3
when:
response.reset()
request.json = [
a:10, b:20, c:30
]
controller.testJson()
then:
response.json.a == 10 // <-- test failed here
response.json.b == 20
response.json.c == 30
}
}
The test will fail with the following error
response.json.a == 10
| | | |
| | 1 false
| [a:1, b:2, c:3]
The question is: how can I reset the state of the request? or why I cannot set new value to request.json?
Updated:
Please check this demo project: https://github.com/jaguar1975cn/grails403test