Polish "Validate excluded autoconfiguration classes"

- Apply code formatting
- Move configuration of excepted exception to immediately before line
  that will throw the exception
- Use String.format with %n to produce platform-specific new lines

See gh-7407

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/EnableAutoConfigurationImportSelector.java

@@ -57,6 +57,7 @@ import org.springframework.util.ClassUtils;
  * @author Phillip Webb
  * @author Andy Wilkinson
  * @author Stephane Nicoll
+ * @author Madhura Bhave
  * @since 1.3.0
  * @see EnableAutoConfiguration
  */
@@ -164,13 +165,14 @@ public class EnableAutoConfigurationImportSelector
 		for (String exclusion : exclusions) {
 			if (ClassUtils.isPresent(exclusion, getClass().getClassLoader())
 					&& !configurations.contains(exclusion)) {
-				message.append("\t- ").append(exclusion).append("\n");
+				message.append("\t- ").append(exclusion).append(String.format("%n"));
 			}
 		}
 		if (!message.toString().isEmpty()) {
-			throw new IllegalStateException(
-					"The following classes could not be excluded because they are not auto-configuration classes:\n"
-							+ message.toString());
+			throw new IllegalStateException(String.format(
+					"The following classes could not be excluded because they are"
+							+ " not auto-configuration classes:%n%s",
+					message.toString()));
 		}
 
 	}

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/EnableAutoConfigurationImportSelectorTests.java

@@ -47,7 +47,7 @@ import static org.mockito.BDDMockito.given;
  *
  * @author Andy Wilkinson
  * @author Stephane Nicoll
- *
+ * @author Madhura Bhave
  */
 public class EnableAutoConfigurationImportSelectorTests {
 
@@ -173,30 +173,31 @@ public class EnableAutoConfigurationImportSelectorTests {
 	}
 
 	@Test
-	public void nonAutoConfigurationClassExclusionsShouldThrowException() throws Exception {
-		this.expected.expect(IllegalStateException.class);
+	public void nonAutoConfigurationClassExclusionsShouldThrowException()
+			throws Exception {
 		configureExclusions(new String[] { TestConfiguration.class.getName() },
 				new String[0], new String[0]);
+		this.expected.expect(IllegalStateException.class);
 		this.importSelector.selectImports(this.annotationMetadata);
 	}
 
 	@Test
 	public void nonAutoConfigurationClassNameExclusionsWhenPresentOnClassPathShouldThrowException()
 			throws Exception {
-		this.expected.expect(IllegalStateException.class);
 		configureExclusions(new String[0],
-				new String[] { "org.springframework.boot.autoconfigure.EnableAutoConfigurationImportSelectorTests.TestConfiguration" },
+				new String[] {
+						"org.springframework.boot.autoconfigure.EnableAutoConfigurationImportSelectorTests.TestConfiguration" },
 				new String[0]);
+		this.expected.expect(IllegalStateException.class);
 		this.importSelector.selectImports(this.annotationMetadata);
 	}
 
 	@Test
 	public void nonAutoConfigurationPropertyExclusionsWhenPresentOnClassPathShouldThrowException()
 			throws Exception {
+		configureExclusions(new String[0], new String[0], new String[] {
+				"org.springframework.boot.autoconfigure.EnableAutoConfigurationImportSelectorTests.TestConfiguration" });
 		this.expected.expect(IllegalStateException.class);
-		configureExclusions(new String[0],
-				new String[0],
-				new String[] { "org.springframework.boot.autoconfigure.EnableAutoConfigurationImportSelectorTests.TestConfiguration" });
 		this.importSelector.selectImports(this.annotationMetadata);
 	}