Add generic check to Require.

The new method `Require.that` checks that the argument is true. If not
an `IllegalArgumentException` is thrown.

Author: cboehme

src/main/java/org/culturegraph/mf/util/Require.java

@@ -75,6 +75,26 @@ public static int notNegative(final int value, final String message) {
 		return value;
 	}
 
+	/**
+	 * Throws an {@link IllegalArgumentException} if {@code condition} is false.
+	 */
+	public static void that(final boolean condition) {
+		that(condition, "parameter is not valid");
+	}
+
+	/**
+	 * Throws an {@link IllegalArgumentException} if {@code condition} is false.
+	 *
+	 * @param message
+	 *            exception message
+	 * @return {@code value}
+	 */
+	private static void that(final boolean condition, final String message) {
+		if (!condition) {
+			throw new IllegalArgumentException(message);
+		}
+	}
+
 	/**
 	 * Throws an {@link IndexOutOfBoundsException} if {@code index} is negative
 	 * or equal to or greater than {@code arrayLength}.

src/test/java/org/culturegraph/mf/util/RequireTest.java

@@ -49,6 +49,16 @@ public void notNegativeShouldReturnArgIfArgIsNotNegative() {
 		assertEquals(0, Require.notNegative(0));
 	}
 
+	@Test(expected = IllegalArgumentException.class)
+	public void thatShouldFailIfArgumentIsFalse() {
+		Require.that(false);
+	}
+
+	@Test
+	public void thatShouldDoNothingIfArgumentIsTrue() {
+		Require.that(true);
+	}
+
 	@Test(expected = IndexOutOfBoundsException.class)
 	public void validArrayIndexShouldThrowIndexOutOfBoundsExceptionIfIndexIsNegative() {
 		Require.validArrayIndex(-1, 2);