Make is easier to use TestRestTemplate with a custom ResponseErrorHandler

[MateuszRasinski]

Custom error handler set using RestTemplateBuilder bean or using the configuration TestRestTemplateConfiguration from Spring Boot Reference Guide is overriden by TestRestTemplate.NoOpResponseErrorHandler.

Specifically, when using the following class:

class CustomResponseErrorHandler extends DefaultResponseErrorHandler {
    // implementation
}

in the configuration of the builder:

ResponseErrorHandler customErrorHandler = new CustomResponseErrorHandler();
RestTemplateBuilder builder = builderProvider.getIfAvailable()
                                             .errorHandler(customErrorHandler);

The following line is false:

new TestRestTemplate(builder.build()).getRestTemplate().getErrorHandler().equals(customErrorHandler)

[wilkinsona]

Closing in favour of the PR (#7266).

[dallasvaughan]

Just a note about this: I discovered this issue when I called the method TestRestTemplate.withBasicAuth(String username, String password).

Inside that method is the call:

restTemplate.setErrorHandler(getRestTemplate().getErrorHandler());

...which sets the new RestTemplate's ErrorHandler with the current one. But then later in the method the TestRestTemplate constructor is called which then (re-)sets the just-set ResponseErrorHandler back to NoOpResponseErrorHandler.

This logic, along with the description in the javadoc for this method (Creates a new {@code TestRestTemplate} with the same configuration as this one), implies that the RestTemplate config should be the same as it was coming in, but it sets it to NoOpResponseErrorHandler regardless of the previous state.

[philwebb]

Thanks @dallasvaughan, I've raised #7441 to fix this.