apps/OboeTester/app/src/main/res/layout/activity_extra_tests.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ExtraTestsActivity">

    <GridLayout
        android:id="@+id/buttonGrid"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:columnCount="2">

    <Button
        android:id="@+id/buttonBackToMain"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_columnWeight="1"
        android:layout_gravity="fill"
        android:backgroundTint="@color/button_tint"
        android:onClick="onLaunchMainActivity"
        android:text="Back to Main" />

    <Button
        android:id="@+id/buttonExternalTap"
        android:layout_gravity="fill"
        android:layout_width="0dp"
        android:layout_columnWeight="1"
        android:layout_height="wrap_content"
        android:backgroundTint="@color/button_tint"
        android:onClick="onLaunchExternalTapTest"
        android:text="External Tap" />

    <Button
        android:id="@+id/buttonPlugLatency"
        android:layout_gravity="fill"
        android:layout_width="0dp"
        android:layout_columnWeight="1"
        android:layout_height="wrap_content"
        android:backgroundTint="@color/button_tint"
        android:onClick="onLaunchPlugLatencyTest"
        android:text="Plug Latency" />

    <Button
        android:id="@+id/buttonErrorCallback"
        android:layout_gravity="fill"
        android:layout_width="0dp"
        android:layout_columnWeight="1"
        android:layout_height="wrap_content"
        android:backgroundTint="@color/button_tint"
        android:onClick="onLaunchErrorCallbackTest"
        android:text="Error Callback" />
</GridLayout>
</android.support.constraint.ConstraintLayout>