Spring Add a method to RestTestClient API that provides a JsonContentAssert

The RestTestClient API provides a .json(String expected) method that allows the entire JSON response to be verified via JSONAssert e.g.

restTestClient.get().uri("/persons/1")
            .exchange()
            .expectStatus().isOk()
            .expectBody()
            .json("""
                {
                  "data": [
                    {"id": "123", "name": "John Doe",  "email": "john@example.com"}
                  ]
                }
            """)

This approach is fine when verifying simple JSON responses, but it becomes unwieldy for more complex JSON responses and/or when we want to compare the JSON properties with Java object properties.

By contrast, the MockMvcTester API provides a bodyJson() method that returns a org.springframework.test.json.JsonContentAssert object that supports more fine-grained assertions, e.g.

mockMvcTester.get().uri("/persons/1")
            .assertThat()
            .hasStatusOk()
            .bodyJson()
            .extractingPath("$.data")
            .asArray().singleElement()
            .hasFieldOrPropertyWithValue("id", expectedUser.getId())
            .hasFieldOrPropertyWithValue("name", expectedUser.getName())
            .hasFieldOrPropertyWithValue("email", expectedUser.getEmail())

Proposal

Add a method toRestTestClient.BodyContentSpec that allows the response to be consumed with a JsonContentAssert, e.g.

restTestClient.get().uri("/persons/1")
            .exchange()
            .expectStatus().isOk()
            .expectBody() 
            .consumeWithJsonAssert((JsonContentAssert jsonContentAssert) -> {
                jsonContentAssert.extractingPath("$.data")
                        .asArray().singleElement()
                        .hasFieldOrPropertyWithValue("id", expectedUser.getId())
                        .hasFieldOrPropertyWithValue("name", expectedUser.getName())
                        .hasFieldOrPropertyWithValue("email", expectedUser.getEmail())
            })

Current Workaround

In the absence of this method, I create the JsonContentAssert as below:

```java restTestClient.get().uri("/persons/1") .exchange() .expectStatus().isOk() .expectBody() .consumeWith(response -> { String responseBody = new String(response.getResponseBody(), Charset.defaultCharset()); JsonContentAssert jsonContentAssert = new JsonContent(responseBody).assertThat(); jsonContentAssert.extractingPath("$.data") .asArray().singleElement() .hasFieldOrPropertyWithValue("id", expectedUser.getId()) .hasFieldOrPropertyWithValue("name", expectedUser.getName()) .hasFieldOrPropertyWithValue("email", expectedUser.getEmail()) });

Comment From: vpelikh

I'm missing the same functionality in WebTestClient. I might work on this once it becomes clear which direction to take.

Comment From: rstoyanchev

Thanks for raising this. We intend a comprehensive update as described in #35701, #35702, and #35703. We're actively working on it, and given the short time remaining, it is not open for pull requests.

Comment From: rstoyanchev

Superseded by #35701 for RestTestClient, and #35737 for WebTestClient.