added append function

src/main/java/strman/Strman.java

@@ -1,9 +1,31 @@
 package strman;
 
+import java.util.StringJoiner;
+
 /**
  * A String manipulation library without any dependencies
  */
 public interface Strman {
 
 
+    /**
+     * Appends Strings to value
+     *
+     * @param value   initial String
+     * @param appends -- an array of strings to append
+     * @return full string
+     */
+    static String append(final String value, final String... appends) throws IllegalArgumentException {
+        if (value == null) {
+            throw new IllegalArgumentException("'value' should be not null.");
+        }
+        if (appends == null || appends.length == 0) {
+            return value;
+        }
+        StringJoiner joiner = new StringJoiner("");
+        for (String append : appends) {
+            joiner.add(append);
+        }
+        return value + joiner.toString();
+    }
 }

src/test/java/strman/StrmanTest.java

@@ -2,9 +2,21 @@ package strman;
 
 import org.junit.Test;
 
-import static org.junit.Assert.*;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.junit.Assert.assertThat;
+import static strman.Strman.append;
 
 public class StrmanTest {
 
+    @Test
+    public void shouldAppendStringsToEndOfValue() throws Exception {
+        assertThat(append("f", "o", "o", "b", "a", "r"), equalTo("foobar"));
+        assertThat(append("foobar"), equalTo("foobar"));
+        assertThat(append("", "foobar"), equalTo("foobar"));
+    }
 
+    @Test(expected = IllegalArgumentException.class)
+    public void appendShouldThrowIllegalArgumentExceptionWhenValueIsNull() throws Exception {
+        append(null);
+    }
 }