Clean up Mockito usage

This commit migrates to the MockitoJUnitRunner where sensible, which
will later allow for an easier migration to Mockito's extension for
JUnit Jupiter.

In addition, this commit deletes unnecessary stubbing for various mocks
and polishes test fixture setup in various test classes.

spring-webflux/src/test/java/org/springframework/web/reactive/config/DelegatingWebFluxConfigurationTests.java

@@ -21,10 +21,11 @@ import java.util.List;
 
 import org.junit.Before;
 import org.junit.Test;
+import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Captor;
 import org.mockito.Mock;
-import org.mockito.MockitoAnnotations;
+import org.mockito.junit.MockitoJUnitRunner;
 
 import org.springframework.context.support.StaticApplicationContext;
 import org.springframework.core.ReactiveAdapterRegistry;
@@ -48,10 +49,9 @@ import static org.mockito.Mockito.verify;
  *
  * @author Brian Clozel
  */
+@RunWith(MockitoJUnitRunner.class)
 public class DelegatingWebFluxConfigurationTests {
 
-	private DelegatingWebFluxConfiguration delegatingConfig;
-
 	@Mock
 	private WebFluxConfigurer webFluxConfigurer;
 
@@ -64,10 +64,11 @@ public class DelegatingWebFluxConfigurationTests {
 	@Captor
 	private ArgumentCaptor<FormatterRegistry> formatterRegistry;
 
+	private DelegatingWebFluxConfiguration delegatingConfig;
+
 
 	@Before
 	public void setup() {
-		MockitoAnnotations.initMocks(this);
 		delegatingConfig = new DelegatingWebFluxConfiguration();
 		delegatingConfig.setApplicationContext(new StaticApplicationContext());
 		given(webFluxConfigurer.getValidator()).willReturn(null);

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/DefaultWebClientTests.java

@@ -23,10 +23,11 @@ import java.util.Map;
 
 import org.junit.Before;
 import org.junit.Test;
+import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Captor;
-import org.mockito.Mockito;
-import org.mockito.MockitoAnnotations;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
 
@@ -39,6 +40,7 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.verifyZeroInteractions;
 
@@ -48,20 +50,20 @@ import static org.mockito.Mockito.verifyZeroInteractions;
  * @author Rossen Stoyanchev
  * @author Brian Clozel
  */
+@RunWith(MockitoJUnitRunner.class)
 public class DefaultWebClientTests {
 
-	private WebClient.Builder builder;
-
+	@Mock
 	private ExchangeFunction exchangeFunction;
 
 	@Captor
 	private ArgumentCaptor<ClientRequest> captor;
 
+	private WebClient.Builder builder;
+
 
 	@Before
 	public void setup() {
-		MockitoAnnotations.initMocks(this);
-		this.exchangeFunction = mock(ExchangeFunction.class);
 		ClientResponse mockResponse = mock(ClientResponse.class);
 		given(this.exchangeFunction.exchange(this.captor.capture())).willReturn(Mono.just(mockResponse));
 		this.builder = WebClient.builder().baseUrl("/base").exchangeFunction(this.exchangeFunction);
@@ -309,7 +311,7 @@ public class DefaultWebClientTests {
 
 	private ClientRequest verifyAndGetRequest() {
 		ClientRequest request = this.captor.getValue();
-		Mockito.verify(this.exchangeFunction).exchange(request);
+		verify(this.exchangeFunction).exchange(request);
 		verifyNoMoreInteractions(this.exchangeFunction);
 		return request;
 	}