Update ParentRunner(TestClass) to check for a null parameter.

Author: kcooney

src/main/java/org/junit/internal/Checks.java

@@ -0,0 +1,37 @@
+package org.junit.internal;
+
+/** @since 4.13 */
+public final class Checks {
+
+    private Checks() {}
+
+    /**
+     * Checks that the given value is not {@code null}.
+     *
+     * @param value object reference to check
+     * @return the passed-in value, if not {@code null}
+     * @throws NullPointerException if {@code value} is {@code null}
+     */
+    public static <T> T notNull(T value) {
+        if (value == null) {
+            throw new NullPointerException();
+        }
+        return value;
+    }
+
+    /**
+     * Checks that the given value is not {@code null}, using the given message
+     * as the exception message if an exception is thrown.
+     *
+     * @param value object reference to check
+     * @param message message to use if {@code value} is {@code null}
+     * @return the passed-in value, if not {@code null}
+     * @throws NullPointerException if {@code value} is {@code null}
+     */
+    public static <T> T notNull(T value, String message) {
+        if (value == null) {
+            throw new NullPointerException(String.valueOf(message));
+        }
+        return value;
+    }
+}

src/main/java/org/junit/runners/ParentRunner.java

@@ -1,5 +1,6 @@
 package org.junit.runners;
 
+import static org.junit.internal.Checks.notNull;
 import static org.junit.internal.runners.rules.RuleMemberValidator.CLASS_RULE_METHOD_VALIDATOR;
 import static org.junit.internal.runners.rules.RuleMemberValidator.CLASS_RULE_VALIDATOR;
 
@@ -92,7 +93,7 @@ protected ParentRunner(Class<?> testClass) throws InitializationError {
     * @since 4.13
     */
     protected ParentRunner(TestClass testClass) throws InitializationError {
-       this.testClass = testClass;
+       this.testClass = notNull(testClass);
        validate();
     }
 

src/main/java/org/junit/runners/parameterized/TestWithParameters.java

@@ -1,6 +1,7 @@
 package org.junit.runners.parameterized;
 
 import static java.util.Collections.unmodifiableList;
+import static org.junit.internal.Checks.notNull;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -73,10 +74,4 @@ public String toString() {
         return testClass.getName() + " '" + name + "' with parameters "
                 + parameters;
     }
-
-    private static void notNull(Object value, String message) {
-        if (value == null) {
-            throw new NullPointerException(message);
-        }
-    }
 }

src/test/java/org/junit/internal/AllInternalTests.java

@@ -13,6 +13,7 @@
 @RunWith(Suite.class)
 @SuiteClasses({
         AnnotatedBuilderTest.class,
+        ChecksTest.class,
         ErrorReportingRunnerTest.class,
         ExpectExceptionTest.class,
         FailOnTimeoutTest.class,

src/test/java/org/junit/internal/ChecksTest.java

@@ -0,0 +1,52 @@
+package org.junit.internal;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.fail;
+import static org.junit.internal.Checks.notNull;
+import org.junit.Test;
+
+/** Tests for {@link Checks}. */
+public class ChecksTest {
+
+    @Test
+    public void notNullShouldReturnNonNullValues() {
+        Double value = Double.valueOf(3.14);
+
+        Double result = notNull(value);
+
+        assertSame(value, result);
+    }
+
+    @Test
+    public void notNullShouldThrowOnNullValues() {
+        try {
+            notNull(null);
+        } catch (NullPointerException e) {
+            assertNull("message should be null", e.getMessage());
+            return;
+        }
+        fail("NullPointerException expected");
+    }
+
+    @Test
+    public void notNullWithMessageShouldReturnNonNullValues() {
+        Float value = Float.valueOf(3.14f);
+
+        Float result = notNull(value, "woops");
+
+        assertSame(value, result);
+    }
+
+    @Test
+    public void notNullWithMessageShouldThrowOnNullValues() {
+        try {
+            notNull(null, "woops");
+        } catch (NullPointerException e) {
+            assertEquals("message does not match", "woops", e.getMessage());
+            return;
+        }
+        fail("NullPointerException expected");
+    }
+}