Add TestableResources

Makes it easy to add or change values of resources from tests.

Test: runtest --path frameworks/base/tests/testables/tests
Change-Id: Iaedff3d4ce9eaf9f270e7c62bc8c1634bd3519ec

tests/testables/src/android/testing/TestableContext.java

@@ -69,6 +69,7 @@ public class TestableContext extends ContextWrapper implements TestRule {
     private LeakCheck.Tracker mReceiver;
     private LeakCheck.Tracker mService;
     private LeakCheck.Tracker mComponent;
+    private TestableResources mTestableResources;
 
     public TestableContext(Context base) {
         this(base, null);
@@ -98,9 +99,37 @@ public class TestableContext extends ContextWrapper implements TestRule {
         return super.getPackageManager();
     }
 
+    /**
+     * Makes sure the resources being returned by this TestableContext are a version of
+     * TestableResources.
+     * @see #getResources()
+     */
+    public void ensureTestableResources() {
+        if (mTestableResources == null) {
+            mTestableResources = new TestableResources(super.getResources());
+        }
+    }
+
+    /**
+     * Get (and create if necessary) {@link TestableResources} for this TestableContext.
+     */
+    public TestableResources getOrCreateTestableResources() {
+        ensureTestableResources();
+        return mTestableResources;
+    }
+
+    /**
+     * Returns a Resources instance for the test.
+     *
+     * By default this returns the same resources object that would come from the
+     * {@link ContextWrapper}, but if {@link #ensureTestableResources()} or
+     * {@link #getOrCreateTestableResources()} has been called, it will return resources gotten from
+     * {@link TestableResources}.
+     */
     @Override
     public Resources getResources() {
-        return super.getResources();
+        return mTestableResources != null ? mTestableResources.getResources()
+                : super.getResources();
     }
 
     public <T> void addMockSystemService(Class<T> service, T mock) {

tests/testables/src/android/testing/TestableResources.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2017 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 android.testing;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.withSettings;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.util.Log;
+import android.util.SparseArray;
+
+import org.mockito.invocation.InvocationOnMock;
+
+/**
+ * Provides a version of Resources that defaults to all existing resources, but can have ids
+ * changed to return specific values.
+ * <p>
+ * TestableResources are lazily initialized, be sure to call
+ * {@link TestableContext#ensureTestableResources} before your tested code has an opportunity
+ * to cache {@link Context#getResources}.
+ * </p>
+ */
+public class TestableResources {
+
+    private static final String TAG = "TestableResources";
+    private final Resources mResources;
+    private final SparseArray<Object> mOverrides = new SparseArray<>();
+
+    TestableResources(Resources realResources) {
+        mResources = mock(Resources.class, withSettings()
+                .spiedInstance(realResources)
+                .defaultAnswer(this::answer));
+    }
+
+    /**
+     * Gets the implementation of Resources that will return overridden values when called.
+     */
+    public Resources getResources() {
+        return mResources;
+    }
+
+    /**
+     * Sets the return value for the specified resource id.
+     * <p>
+     * Since resource ids are unique there is a single addOverride that will override the value
+     * whenever it is gotten regardless of which method is used (i.e. getColor or getDrawable).
+     * </p>
+     * @param id The resource id to be overridden
+     * @param value The value of the resource, null to cause a {@link Resources.NotFoundException}
+     *              when gotten.
+     */
+    public void addOverride(int id, Object value) {
+        mOverrides.put(id, value);
+    }
+
+    /**
+     * Removes the override for the specified id.
+     * <p>
+     * This should be called over addOverride(id, null), because specifying a null value will
+     * cause a {@link Resources.NotFoundException} whereas removing the override will actually
+     * switch back to returning the default/real value of the resource.
+     * </p>
+     * @param id
+     */
+    public void removeOverride(int id) {
+        mOverrides.remove(id);
+    }
+
+    private Object answer(InvocationOnMock invocationOnMock) throws Throwable {
+        try {
+            int id = invocationOnMock.getArgument(0);
+            int index = mOverrides.indexOfKey(id);
+            if (index >= 0) {
+                Object value = mOverrides.valueAt(index);
+                if (value == null) throw new Resources.NotFoundException();
+                return value;
+            }
+        } catch (Resources.NotFoundException e) {
+            // Let through NotFoundException.
+            throw e;
+        } catch (Throwable t) {
+            // Generic catching for the many things that can go wrong, fall back to
+            // the real implementation.
+            Log.i(TAG, "Falling back to default resources call " + t);
+        }
+        return invocationOnMock.callRealMethod();
+    }
+}

tests/testables/tests/res/values/strings.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+/**
+ * Copyright (c) 2009, 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.
+ */
+-->
+<resources xmlns:xliff="urn:oasis:names:tc:xliff:document:1.2">
+    <string name="test_string">This is a test string</string>
+</resources>

tests/testables/tests/src/android/testing/TestableResourcesTest.java

@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2017 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 android.testing;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.fail;
+
+import android.content.res.Resources;
+import android.support.test.InstrumentationRegistry;
+
+import com.android.testables.R;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+@RunWith(AndroidTestingRunner.class)
+public class TestableResourcesTest {
+
+    @Rule
+    public TestableContext mContext = new TestableContext(InstrumentationRegistry.getContext());
+
+    @Test
+    public void testLazyInit() {
+        Resources before = mContext.getResources();
+        mContext.ensureTestableResources();
+        Resources after = mContext.getResources();
+        assertNotEquals(before, after);
+    }
+
+    @Test
+    public void testAddingResource() {
+        final int nonExistentId = 3; // Ids don't go this low.
+
+        try {
+            mContext.getColor(nonExistentId);
+            fail("Should throw NotFoundException");
+        } catch (Resources.NotFoundException e) {
+        }
+        mContext.getOrCreateTestableResources().addOverride(nonExistentId, 0xffffff);
+
+        assertEquals(0xffffff, mContext.getColor(nonExistentId));
+    }
+
+    @Test
+    public void testClearingResource() {
+        final int nonExistentId = 3; // Ids don't go this low.
+
+        mContext.getOrCreateTestableResources().addOverride(nonExistentId, 0xffffff);
+        assertEquals(0xffffff, mContext.getColor(nonExistentId));
+        mContext.getOrCreateTestableResources().removeOverride(nonExistentId);
+        try {
+            mContext.getColor(nonExistentId);
+            fail("Should throw NotFoundException");
+        } catch (Resources.NotFoundException e) {
+        }
+    }
+
+    @Test
+    public void testOverrideExisting() {
+        int existentId = R.string.test_string;
+
+        assertNotNull(mContext.getString(existentId));
+        mContext.getOrCreateTestableResources().addOverride(existentId, "Other strings");
+
+        assertEquals("Other strings", mContext.getString(existentId));
+    }
+
+    @Test(expected = Resources.NotFoundException.class)
+    public void testNonExistentException() {
+        int existentId = R.string.test_string;
+
+        assertNotNull(mContext.getString(existentId));
+        mContext.getOrCreateTestableResources().addOverride(existentId, null);
+
+        assertNull(mContext.getString(existentId));
+    }
+}