libs/ui: Add MockFence

Add a MockFence class to allow unit tests to mock fences.

Change-Id: I37cf6ce77cb446179b73dfc21f79b19eba2be58f
diff --git a/libs/ui/tests/Android.bp b/libs/ui/tests/Android.bp
index 516aad8..a87740a 100644
--- a/libs/ui/tests/Android.bp
+++ b/libs/ui/tests/Android.bp
@@ -115,3 +115,12 @@
     srcs: ["Size_test.cpp"],
     cflags: ["-Wall", "-Werror"],
 }
+
+cc_test {
+    name: "MockFence_test",
+    shared_libs: ["libui"],
+    static_libs: ["libgmock"],
+    srcs: ["MockFence_test.cpp"],
+    cflags: ["-Wall", "-Werror"],
+}
+
diff --git a/libs/ui/tests/MockFence_test.cpp b/libs/ui/tests/MockFence_test.cpp
new file mode 100644
index 0000000..6e520b1
--- /dev/null
+++ b/libs/ui/tests/MockFence_test.cpp
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2021 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.
+ */
+
+#include <ui/MockFence.h>
+
+#include <gtest/gtest.h>
+
+namespace android::ui {
+
+using testing::Return;
+
+class MockFenceTest : public testing::Test {
+public:
+    sp<Fence> getFenceForTesting() const { return mMockFence; }
+
+    const mock::MockFence& getMockFence() const { return *mMockFence; }
+
+private:
+    sp<mock::MockFence> mMockFence = sp<mock::MockFence>::make();
+};
+
+TEST_F(MockFenceTest, getSignalTime) {
+    sp<Fence> fence = getFenceForTesting();
+
+    EXPECT_CALL(getMockFence(), getSignalTime).WillOnce(Return(Fence::SIGNAL_TIME_PENDING));
+    EXPECT_EQ(Fence::SIGNAL_TIME_PENDING, fence->getSignalTime());
+
+    EXPECT_CALL(getMockFence(), getSignalTime).WillOnce(Return(1234));
+    EXPECT_EQ(1234, fence->getSignalTime());
+}
+
+} // namespace android::ui