Add a test case to demonstrate MessageDigest.reset() doesn't.

Uncovered by a more general test:
  org.apache.harmony.security.tests.java.security.MessageDigest2Test#test_digest
diff --git a/luni/src/test/java/libcore/java/security/MessageDigestTest.java b/luni/src/test/java/libcore/java/security/MessageDigestTest.java
new file mode 100644
index 0000000..0e55428
--- /dev/null
+++ b/luni/src/test/java/libcore/java/security/MessageDigestTest.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package libcore.java.security;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Arrays;
+import junit.framework.TestCase;
+
+public final class MessageDigestTest extends TestCase {
+
+    private final byte[] sha_456 = {
+            -24,   9, -59, -47,  -50,  -92, 123, 69, -29,  71,
+              1, -46,  63,  96, -118, -102,  88,  3,  77, -55
+    };
+
+    public void testShaReset() throws NoSuchAlgorithmException {
+        MessageDigest sha = MessageDigest.getInstance("SHA");
+        sha.update(new byte[] { 1, 2, 3 });
+        sha.reset();
+        sha.update(new byte[] { 4, 5, 6 });
+        assertEquals(Arrays.toString(sha_456), Arrays.toString(sha.digest()));
+    }
+}