Proper Javadoc example / add test for StringUtils

- Proper example for the purpose of javadoc and how it could look like
- Fix containsAny to be null safe
- Add tests

src/main/java/fr/xephi/authme/util/StringUtils.java

@@ -5,17 +5,18 @@ import net.ricecode.similarity.StringSimilarityService;
 import net.ricecode.similarity.StringSimilarityServiceImpl;
 
 /**
+ * Utility class for String operations.
  */
 public class StringUtils {
 
     /**
      * Get the difference of two strings.
      *
-     * @param first First string.
-     * @param second Second string.
+     * @param first First string
+     * @param second Second string
      *
-    
-     * @return The difference value. */
+     * @return The difference value
+     */
     public static double getDifference(String first, String second) {
         // Make sure the strings are valid.
         if(first == null || second == null)
@@ -27,22 +28,25 @@ public class StringUtils {
         // Determine the difference value, return the result
         return Math.abs(service.score(first, second) - 1.0);
     }
-    
+
     /**
-     * Method containsAny.
-     * @param str String
-     * @param pieces String[]
-    
-     * @return boolean */
+     * Returns whether the given string contains any of the provided elements.
+     *
+     * @param str the string to analyze
+     * @param pieces the items to check the string for
+     *
+     * @return true if the string contains at least one of the items
+     */
     public static boolean containsAny(String str, String... pieces) {
     	if (str == null) {
     		return false;
     	}
     	for (String piece : pieces) {
-    		if (str.contains(piece)) {
+    		if (piece != null && str.contains(piece)) {
     			return true;
     		}
     	}
     	return false;
     }
+
 }

src/test/java/fr/xephi/authme/util/StringUtilsTest.java

@@ -0,0 +1,46 @@
+package fr.xephi.authme.util;
+
+import org.junit.Test;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.junit.Assert.assertThat;
+
+/**
+ * Test for {@link StringUtils}.
+ */
+public class StringUtilsTest {
+
+    @Test
+    public void shouldFindContainedItem() {
+        // given
+        String text = "This is a test of containsAny()";
+        String piece = "test";
+
+        // when
+        boolean result = StringUtils.containsAny(text, "some", "words", "that", "do not", "exist", piece);
+
+        // then
+        assertThat(result, equalTo(true));
+    }
+
+    @Test
+    public void shouldReturnFalseIfNoneFound() {
+        // given
+        String text = "This is a test string";
+
+        // when
+        boolean result = StringUtils.containsAny(text, "some", "other", "words", null);
+
+        // then
+        assertThat(result, equalTo(false));
+    }
+
+    @Test
+    public void shouldReturnFalseForNullString() {
+        // given/when
+        boolean result = StringUtils.containsAny(null, "some", "words", "to", "check");
+
+        // then
+        assertThat(result, equalTo(false));
+    }
+}