Return original object in Preconditions

The commit updates the Preconditions class so that its methods return
the original object in case of a successful check. In addition, various
clients of the Preconditions API have been updated to make use of this
new feature.

Issue: #95

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junit-commons/src/main/java/org/junit/gen5/commons/util/Preconditions.java

@@ -38,86 +38,106 @@ private Preconditions() {
 	 * Assert that the supplied {@link Object} is not {@code null}.
 	 *
 	 * @param object the object to check
-	 * @param message precondition failure message
+	 * @param message precondition violation message
+	 * @return the supplied object as a convenience
+	 * @throws IllegalArgumentException if the supplied object is {@code null}
 	 * @see #notNull(Object, Supplier)
 	 */
-	public static void notNull(Object object, String message) throws IllegalArgumentException {
-		notNull(object, () -> message);
+	public static <T extends Object> T notNull(T object, String message) throws IllegalArgumentException {
+		return notNull(object, () -> message);
 	}
 
 	/**
 	 * Assert that the supplied {@link Object} is not {@code null}.
 	 *
 	 * @param object the object to check
-	 * @param messageSupplier precondition failure message supplier
+	 * @param messageSupplier precondition violation message supplier
+	 * @return the supplied object as a convenience
+	 * @throws IllegalArgumentException if the supplied object is {@code null}
 	 * @see #condition(boolean, Supplier)
 	 */
-	public static void notNull(Object object, Supplier<String> messageSupplier) throws IllegalArgumentException {
+	public static <T extends Object> T notNull(T object, Supplier<String> messageSupplier)
+			throws IllegalArgumentException {
 		condition(object != null, messageSupplier);
+		return object;
 	}
 
 	/**
 	 * Assert that the supplied {@link String} is not {@code null} or empty.
 	 *
 	 * @param str the string to check
-	 * @param message precondition failure message
+	 * @param message precondition violation message
+	 * @return the supplied string as a convenience
+	 * @throws IllegalArgumentException if the supplied string is {@code null} or empty
 	 * @see #notEmpty(String, Supplier)
 	 */
-	public static void notEmpty(String str, String message) throws IllegalArgumentException {
-		notEmpty(str, () -> message);
+	public static String notEmpty(String str, String message) throws IllegalArgumentException {
+		return notEmpty(str, () -> message);
 	}
 
 	/**
 	 * Assert that the supplied {@link String} is not {@code null} or empty.
 	 *
 	 * @param str the string to check
-	 * @param messageSupplier precondition failure message supplier
+	 * @param messageSupplier precondition violation message supplier
+	 * @return the supplied string as a convenience
+	 * @throws IllegalArgumentException if the supplied string is {@code null} or empty
 	 * @see StringUtils#isNotEmpty(CharSequence)
 	 * @see #condition(boolean, Supplier)
 	 */
-	public static void notEmpty(String str, Supplier<String> messageSupplier) throws IllegalArgumentException {
+	public static String notEmpty(String str, Supplier<String> messageSupplier) throws IllegalArgumentException {
 		condition(StringUtils.isNotEmpty(str), messageSupplier);
+		return str;
 	}
 
 	/**
 	 * Assert that the supplied {@link Collection} is not {@code null} or empty.
 	 *
 	 * @param collection the collection to check
-	 * @param message precondition failure message
+	 * @param message precondition violation message
+	 * @return the supplied collection as a convenience
+	 * @throws IllegalArgumentException if the supplied collection is {@code null} or empty
 	 * @see #condition(boolean, Supplier)
 	 */
-	public static void notEmpty(Collection<?> collection, String message) throws IllegalArgumentException {
+	public static <T extends Collection<?>> T notEmpty(T collection, String message) throws IllegalArgumentException {
 		condition(collection != null && !collection.isEmpty(), () -> message);
+		return collection;
 	}
 
 	/**
 	 * Assert that the supplied {@link String} is not {@code null} or blank.
 	 *
 	 * @param str the string to check
-	 * @param message precondition failure message
+	 * @param message precondition violation message
+	 * @return the supplied string as a convenience
+	 * @throws IllegalArgumentException if the supplied string is {@code null} or blank
 	 * @see #notBlank(String, Supplier)
 	 */
-	public static void notBlank(String str, String message) throws IllegalArgumentException {
-		notBlank(str, () -> message);
+	public static String notBlank(String str, String message) throws IllegalArgumentException {
+		return notBlank(str, () -> message);
 	}
 
 	/**
 	 * Assert that the supplied {@link String} is not {@code null} or blank.
 	 *
 	 * @param str the string to check
-	 * @param messageSupplier precondition failure message supplier
+	 * @param messageSupplier precondition violation message supplier
+	 * @return the supplied string as a convenience
+	 * @throws IllegalArgumentException if the supplied string is {@code null} or blank
 	 * @see StringUtils#isNotBlank(String)
 	 * @see #condition(boolean, Supplier)
 	 */
-	public static void notBlank(String str, Supplier<String> messageSupplier) throws IllegalArgumentException {
+	public static String notBlank(String str, Supplier<String> messageSupplier) throws IllegalArgumentException {
 		condition(StringUtils.isNotBlank(str), messageSupplier);
+		return str;
 	}
 
 	/**
 	 * Assert that the supplied {@code predicate} is {@code true}.
 	 *
 	 * @param predicate the predicate to check
-	 * @param message precondition failure message
+	 * @param message precondition violation message
+	 * @throws IllegalArgumentException if the predicate is {@code false}
 	 * @see #condition(boolean, Supplier)
 	 */
 	public static void condition(boolean predicate, String message) throws IllegalArgumentException {
@@ -128,7 +148,7 @@ public static void condition(boolean predicate, String message) throws IllegalAr
 	 * Assert that the supplied {@code predicate} is {@code true}.
 	 *
 	 * @param predicate the predicate to check
-	 * @param messageSupplier precondition failure message supplier
+	 * @param messageSupplier precondition violation message supplier
 	 * @throws IllegalArgumentException if the predicate is {@code false}
 	 */
 	public static void condition(boolean predicate, Supplier<String> messageSupplier) throws IllegalArgumentException {

junit-commons/src/main/java/org/junit/gen5/commons/util/ToStringBuilder.java

@@ -36,13 +36,11 @@ public class ToStringBuilder {
 	private final List<String> values = new ArrayList<>();
 
 	public ToStringBuilder(Object obj) {
-		Preconditions.notNull(obj, "Object must not be null");
-		this.type = obj.getClass();
+		this.type = Preconditions.notNull(obj, "Object must not be null").getClass();
 	}
 
 	public ToStringBuilder(Class<?> type) {
-		Preconditions.notNull(type, "Class must not be null");
-		this.type = type;
+		this.type = Preconditions.notNull(type, "Class must not be null");
 	}
 
 	public ToStringBuilder append(String name, Object value) {

junit-engine-api/src/main/java/org/junit/gen5/engine/AbstractTestDescriptor.java

@@ -34,8 +34,7 @@ public abstract class AbstractTestDescriptor implements TestDescriptor {
 	private final Set<TestDescriptor> children = new LinkedHashSet<>();
 
 	protected AbstractTestDescriptor(String uniqueId) {
-		Preconditions.notBlank(uniqueId, "uniqueId must not be null or empty");
-		this.uniqueId = uniqueId;
+		this.uniqueId = Preconditions.notBlank(uniqueId, "uniqueId must not be null or empty");
 	}
 
 	@Override
@@ -94,8 +93,7 @@ public Set<? extends TestDescriptor> getChildren() {
 	}
 
 	protected final void setSource(TestSource source) {
-		Preconditions.notNull(source, "test source must not be null");
-		this.source = source;
+		this.source = Preconditions.notNull(source, "TestSource must not be null");
 	}
 
 	@Override

junit-engine-api/src/main/java/org/junit/gen5/engine/FileSystemSource.java

@@ -28,8 +28,8 @@ public FileSystemSource(File sourceFileOrDirectory) {
 	}
 
 	public FileSystemSource(File sourceFileOrDirectory, FilePosition positionInFile) {
-		Preconditions.notNull(sourceFileOrDirectory, "source file or directory must not be null");
-		this.sourceFileOrDirectory = sourceFileOrDirectory;
+		this.sourceFileOrDirectory = Preconditions.notNull(sourceFileOrDirectory,
+			"source file or directory must not be null");
 		this.positionInFile = positionInFile;
 	}
 

junit-engine-api/src/main/java/org/junit/gen5/engine/TestExecutionResult.java

@@ -44,8 +44,7 @@ public static TestExecutionResult failed(Throwable throwable) {
 	}
 
 	public TestExecutionResult(Status status, Throwable throwable) {
-		Preconditions.notNull(status, "status must not be null");
-		this.status = status;
+		this.status = Preconditions.notNull(status, "Status must not be null");
 		this.throwable = throwable;
 	}
 

junit-launcher/src/main/java/org/junit/gen5/launcher/TestId.java

@@ -27,8 +27,7 @@ public final class TestId implements Serializable {
 	private final String uniqueId;
 
 	TestId(String uniqueId) {
-		Preconditions.notNull(uniqueId, "uniqueId must not be null");
-		this.uniqueId = uniqueId;
+		this.uniqueId = Preconditions.notBlank(uniqueId, "uniqueId must not be null or empty");
 	}
 
 	@Override
@@ -42,12 +41,12 @@ public boolean equals(Object obj) {
 
 	@Override
 	public int hashCode() {
-		return uniqueId.hashCode();
+		return this.uniqueId.hashCode();
 	}
 
 	@Override
 	public String toString() {
-		return uniqueId;
+		return this.uniqueId;
 	}
 
 }

junit5-engine/src/main/java/org/junit/gen5/engine/junit5/descriptor/ClassTestDescriptor.java

@@ -64,9 +64,7 @@ public class ClassTestDescriptor extends JUnit5TestDescriptor implements Contain
 	ClassTestDescriptor(String uniqueId, Class<?> testClass) {
 		super(uniqueId);
 
-		Preconditions.notNull(testClass, "Class must not be null");
-
-		this.testClass = testClass;
+		this.testClass = Preconditions.notNull(testClass, "Class must not be null");
 		this.displayName = determineDisplayName(testClass, testClass.getName());
 
 		setSource(new JavaSource(testClass));

junit5-engine/src/main/java/org/junit/gen5/engine/junit5/descriptor/JUnit5TestableFactory.java

@@ -45,7 +45,7 @@ JUnit5Testable fromUniqueId(String uniqueId, String engineId) {
 	}
 
 	JUnit5Testable fromClass(Class<?> clazz, String engineId) {
-		Preconditions.notNull(clazz, "clazz must not be null");
+		Preconditions.notNull(clazz, "Class must not be null");
 		Preconditions.notBlank(engineId, "Engine ID must not be null or empty");
 		if (isPotentialTestContainer.test(clazz)) {
 			String uniqueId = engineId + ":" + clazz.getName();

junit5-engine/src/main/java/org/junit/gen5/engine/junit5/descriptor/MethodTestDescriptor.java

@@ -49,11 +49,8 @@ public class MethodTestDescriptor extends JUnit5TestDescriptor implements Leaf<J
 	MethodTestDescriptor(String uniqueId, Class<?> testClass, Method testMethod) {
 		super(uniqueId);
 
-		Preconditions.notNull(testClass, "Class must not be null");
-		Preconditions.notNull(testMethod, "Method must not be null");
-
-		this.testClass = testClass;
-		this.testMethod = testMethod;
+		this.testClass = Preconditions.notNull(testClass, "Class must not be null");
+		this.testMethod = Preconditions.notNull(testMethod, "Method must not be null");
 		this.displayName = determineDisplayName(testMethod, testMethod.getName());
 
 		setSource(new JavaSource(testMethod));