unit tests: added direct AAudio test

Update testFlowgraph
diff --git a/tests/testAAudio.cpp b/tests/testAAudio.cpp
new file mode 100644
index 0000000..62558f3
--- /dev/null
+++ b/tests/testAAudio.cpp
@@ -0,0 +1,64 @@
+#include <oboe/Oboe.h>/*
+ * Copyright 2018 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 <gtest/gtest.h>
+#include <oboe/Oboe.h>
+#include "../src/aaudio/AAudioLoader.h"
+
+using namespace oboe;
+
+class AAudioDirect : public ::testing::Test {
+public:
+    void createBuilder() {
+        mAAudioLoader = AAudioLoader::getInstance();
+        ASSERT_NE(mAAudioLoader, nullptr);
+        ASSERT_EQ(0, mAAudioLoader->open());
+        ASSERT_NE(mAAudioLoader->createStreamBuilder, nullptr);
+        aaudio_result_t result = mAAudioLoader->createStreamBuilder(&mBuilder);
+        ASSERT_NE(mBuilder, nullptr);
+        ASSERT_EQ(result, 0);
+    }
+
+    void openCloseStream() {
+        AAudioStream *stream = nullptr;
+        aaudio_result_t result = mAAudioLoader->builder_openStream(mBuilder, &stream);
+        ASSERT_EQ(result, 0);
+        ASSERT_NE(stream, nullptr);
+
+        result = mAAudioLoader->stream_close(stream);
+        ASSERT_EQ(result, 0);
+    }
+
+    AAudioStreamBuilder *mBuilder = nullptr;
+    AAudioLoader *mAAudioLoader = nullptr;
+};
+
+TEST_F(AAudioDirect, InstantiateAAudioLoader){
+AAudioLoader *aaudioLoader = AAudioLoader::getInstance();
+ASSERT_NE(aaudioLoader, nullptr);
+}
+
+TEST_F(AAudioDirect, OpenCloseHighLatencyStream){
+    createBuilder();
+    mAAudioLoader->builder_setPerformanceMode(mBuilder, AAUDIO_PERFORMANCE_MODE_NONE);
+    openCloseStream();
+}
+
+TEST_F(AAudioDirect, OpenCloseLowLatencyStream){
+    createBuilder();
+    mAAudioLoader->builder_setPerformanceMode(mBuilder, AAUDIO_PERFORMANCE_MODE_LOW_LATENCY);
+    openCloseStream();
+}