Allow MockitoBean to create a mock for a bean that does not exist

This commit aligns the by-type lookup for bean overrides with what was
done when a bean name is present. It now correctly generate a bean
name rather than failing because no bean of that type exists.

Closes gh-32990

spring-test/src/test/java/org/springframework/test/context/bean/override/convention/FailingTestBeanByTypeIntegrationTests.java

@@ -51,8 +51,8 @@ class FailingTestBeanByTypeIntegrationTests {
 				cause(
 					instanceOf(IllegalStateException.class),
 					message("""
-						Unable to select a bean definition to override: found 0 bean definitions \
-						of type %s (as required by annotated field '%s.example')"""
+						Unable to override bean: no bean definitions of type \
+						%s (as required by annotated field '%s.example')"""
 							.formatted(ExampleService.class.getName(), testClass.getSimpleName())))));
 	}
 

spring-test/src/test/java/org/springframework/test/context/bean/override/mockito/FailingMockitoBeanByTypeIntegrationTests.java

@@ -43,19 +43,6 @@ import static org.junit.platform.testkit.engine.TestExecutionResultConditions.me
  */
 class FailingMockitoBeanByTypeIntegrationTests {
 
-	@Test
-	void zeroCandidates() {
-		Class<?> testClass = ZeroCandidatesTestCase.class;
-		EngineTestKitUtils.executeTestsForClass(testClass).assertThatEvents().haveExactly(1,
-			finishedWithFailure(
-				cause(
-					instanceOf(IllegalStateException.class),
-					message("""
-						Unable to select a bean definition to override: found 0 bean definitions \
-						of type %s (as required by annotated field '%s.example')"""
-							.formatted(ExampleService.class.getName(), testClass.getSimpleName())))));
-	}
-
 	@Test
 	void tooManyCandidates() {
 		Class<?> testClass = TooManyCandidatesTestCase.class;
@@ -70,22 +57,6 @@ class FailingMockitoBeanByTypeIntegrationTests {
 	}
 
 
-	@SpringJUnitConfig
-	static class ZeroCandidatesTestCase {
-
-		@MockitoBean
-		ExampleService example;
-
-		@Test
-		void test() {
-			assertThat(example).isNotNull();
-		}
-
-		@Configuration
-		static class Config {
-		}
-	}
-
 	@SpringJUnitConfig
 	static class TooManyCandidatesTestCase {
 

spring-test/src/test/java/org/springframework/test/context/bean/override/mockito/MockitoBeanByTypeIntegrationTests.java

@@ -49,6 +49,9 @@ import static org.mockito.Mockito.verifyNoMoreInteractions;
 @SpringJUnitConfig
 public class MockitoBeanByTypeIntegrationTests {
 
+	@MockitoBean
+	AnotherService serviceIsNotABean;
+
 	@MockitoBean
 	ExampleService anyNameForService;
 
@@ -60,6 +63,17 @@ public class MockitoBeanByTypeIntegrationTests {
 	@CustomQualifier
 	StringBuilder ambiguousMeta;
 
+	@Test
+	void mockIsCreatedWhenNoCandidateIsFound() {
+		assertThat(this.serviceIsNotABean)
+				.satisfies(o -> assertThat(Mockito.mockingDetails(o).isMock()).as("isMock").isTrue());
+
+		when(this.serviceIsNotABean.hello()).thenReturn("Mocked hello");
+
+		assertThat(this.serviceIsNotABean.hello()).isEqualTo("Mocked hello");
+		verify(this.serviceIsNotABean, times(1)).hello();
+		verifyNoMoreInteractions(this.serviceIsNotABean);
+	}
 
 	@Test
 	void overrideIsFoundByType(ApplicationContext ctx) {
@@ -109,6 +123,11 @@ public class MockitoBeanByTypeIntegrationTests {
 		verifyNoMoreInteractions(this.ambiguousMeta);
 	}
 
+	interface AnotherService {
+
+		String hello();
+
+	}
 
 	@Configuration
 	static class Config {