[CODEC-263] test for user reported issue (#240)

* test for user reported issue

* test isBase64

* Add Javadoc

* Fix whitespace

---------

Co-authored-by: Gary Gregory <garydgregory@users.noreply.github.com>

Author: elharo

src/test/java/org/apache/commons/codec/binary/Base64Test.java

@@ -1403,6 +1403,14 @@ public void testUrlSafe() {
 
     }
 
+    /**
+     * Tests <a href="https://issues.apache.org/jira/browse/CODEC-263">CODEC-263</a>.
+     */
+    public void testCodec263() {
+      Base64.decodeBase64("publishMessage");
+      assertTrue(Base64.isBase64("publishMessage"));
+    }
+
     /**
      * Base64 encoding of UUID's is a common use-case, especially in URL-SAFE
      * mode. This test case ends up being the "URL-SAFE" JUnit's.