Make KeyChainActivity.onBackPressed return null response

Also add some negative permissions tests to KeyChainServiceTest

Change-Id: I17d8c5e624db71b45f70c7c46ed49b8571ce323b
diff --git a/src/com/android/keychain/KeyChainActivity.java b/src/com/android/keychain/KeyChainActivity.java
index 3952dfa..f637b09 100644
--- a/src/com/android/keychain/KeyChainActivity.java
+++ b/src/com/android/keychain/KeyChainActivity.java
@@ -162,6 +162,10 @@
         finish();
     }
 
+    @Override public void onBackPressed() {
+        finish(null);
+    }
+
     @Override protected void onSaveInstanceState(Bundle savedState) {
         super.onSaveInstanceState(savedState);
         if (mState != State.INITIAL) {
diff --git a/tests/src/com/android/keychain/tests/KeyChainServiceTest.java b/tests/src/com/android/keychain/tests/KeyChainServiceTest.java
index 3563df2..9da9834 100644
--- a/tests/src/com/android/keychain/tests/KeyChainServiceTest.java
+++ b/tests/src/com/android/keychain/tests/KeyChainServiceTest.java
@@ -236,6 +236,7 @@
             assertNotNull(authToken);
             assertFalse(authToken.isEmpty());
 
+            Log.d(TAG, "test_KeyChainService positive testing");
             byte[] privateKey = mService.getPrivateKey(alias1, authToken);
             assertNotNull(privateKey);
             assertEquals(Arrays.toString(pke1.getPrivateKey().getEncoded()),
@@ -246,6 +247,19 @@
             assertEquals(Arrays.toString(pke1.getCertificate().getEncoded()),
                          Arrays.toString(certificate));
 
+            Log.d(TAG, "test_KeyChainService negative testing");
+            try {
+                mService.getPrivateKey(alias2, authToken);
+                fail();
+            } catch (IllegalStateException expected) {
+            }
+
+            try {
+                mService.getCertificate(alias2, authToken);
+                fail();
+            } catch (IllegalStateException expected) {
+            }
+
             Log.d(TAG, "test_KeyChainService unbind");
             unbindServices();
             assertFalse(mIsBoundSupport);