Move backported JUnit file to third_party

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177637931

third_party/junit/google/registry/testing/JUnitBackports.java

@@ -0,0 +1,122 @@
+package google.registry.testing;
+
+/**
+ * A testing utility class that contains backports of useful but not yet released JUnit methods.
+ *
+ * <p>All of this code was taken directly from
+ * https://github.com/junit-team/junit4/blob/a832c5afe5b0e7c2590d057a1a49a344d207f8a0/src/main/java/org/junit/Assert.java
+ */
+public class JUnitBackports {
+  // TODO(b/68257761): Delete these and switch over to JUnit 4.13 methods upon release.
+
+  /**
+   * This interface facilitates the use of expectThrows from Java 8. It allows method references to
+   * void methods (that declare checked exceptions) to be passed directly into expectThrows without
+   * wrapping. It is not meant to be implemented directly.
+   *
+   * @since 4.13
+   */
+  public interface ThrowingRunnable {
+    void run() throws Throwable;
+  }
+
+  /**
+   * Asserts that {@code runnable} throws an exception of type {@code expectedThrowable} when
+   * executed. If it does not throw an exception, an {@link AssertionError} is thrown. If it throws
+   * the wrong type of exception, an {@code AssertionError} is thrown describing the mismatch; the
+   * exception that was actually thrown can be obtained by calling {@link AssertionError#getCause}.
+   *
+   * @param expectedThrowable the expected type of the exception
+   * @param runnable a function that is expected to throw an exception when executed
+   * @since 4.13
+   */
+  public static void assertThrows(
+      Class<? extends Throwable> expectedThrowable, ThrowingRunnable runnable) {
+    expectThrows(expectedThrowable, runnable);
+  }
+
+  /**
+   * Asserts that {@code runnable} throws an exception of type {@code expectedThrowable} when
+   * executed. If it does, the exception object is returned. If it does not throw an exception, an
+   * {@link AssertionError} is thrown. If it throws the wrong type of exception, an {@code
+   * AssertionError} is thrown describing the mismatch; the exception that was actually thrown can
+   * be obtained by calling {@link AssertionError#getCause}.
+   *
+   * @param expectedThrowable the expected type of the exception
+   * @param runnable a function that is expected to throw an exception when executed
+   * @return the exception thrown by {@code runnable}
+   * @since 4.13
+   */
+  public static <T extends Throwable> T expectThrows(
+      Class<T> expectedThrowable, ThrowingRunnable runnable) {
+    try {
+      runnable.run();
+    } catch (Throwable actualThrown) {
+      if (expectedThrowable.isInstance(actualThrown)) {
+        @SuppressWarnings("unchecked")
+        T retVal = (T) actualThrown;
+        return retVal;
+      } else {
+        String expected = formatClass(expectedThrowable);
+        Class<? extends Throwable> actualThrowable = actualThrown.getClass();
+        String actual = formatClass(actualThrowable);
+        if (expected.equals(actual)) {
+          // There must be multiple class loaders. Add the identity hash code so the message
+          // doesn't say "expected: java.lang.String<my.package.MyException> ..."
+          expected += "@" + Integer.toHexString(System.identityHashCode(expectedThrowable));
+          actual += "@" + Integer.toHexString(System.identityHashCode(actualThrowable));
+        }
+        String mismatchMessage = format("unexpected exception type thrown;", expected, actual);
+
+        // The AssertionError(String, Throwable) ctor is only available on JDK7.
+        AssertionError assertionError = new AssertionError(mismatchMessage);
+        assertionError.initCause(actualThrown);
+        throw assertionError;
+      }
+    }
+    String message =
+        String.format(
+            "expected %s to be thrown, but nothing was thrown", formatClass(expectedThrowable));
+    throw new AssertionError(message);
+  }
+
+  static String format(String message, Object expected, Object actual) {
+    String formatted = "";
+    if (message != null && !"".equals(message)) {
+      formatted = message + " ";
+    }
+    String expectedString = String.valueOf(expected);
+    String actualString = String.valueOf(actual);
+    if (equalsRegardingNull(expectedString, actualString)) {
+      return formatted
+          + "expected: "
+          + formatClassAndValue(expected, expectedString)
+          + " but was: "
+          + formatClassAndValue(actual, actualString);
+    } else {
+      return formatted + "expected:<" + expectedString + "> but was:<" + actualString + ">";
+    }
+  }
+
+  private static String formatClass(Class<?> value) {
+    String className = value.getCanonicalName();
+    return className == null ? value.getName() : className;
+  }
+
+  private static String formatClassAndValue(Object value, String valueString) {
+    String className = value == null ? "null" : value.getClass().getName();
+    return className + "<" + valueString + ">";
+  }
+
+  private static boolean equalsRegardingNull(Object expected, Object actual) {
+    if (expected == null) {
+      return actual == null;
+    }
+
+    return isEquals(expected, actual);
+  }
+
+  private static boolean isEquals(Object expected, Object actual) {
+    return expected.equals(actual);
+  }
+}