Update battery saver footer to have learn more link

This will allow tapping on the Learn More text to take a user to
the support page for battery saver.

Bug: 129010739
Test: atest BatterySaverSettingsTest
Change-Id: Ifb758ea8c608a4051c093b5d1d43f9a039ab1294

tests/robotests/src/com/android/settings/fuelgauge/batterysaver/BatterySaverSettingsTest.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2019 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 com.android.settings.fuelgauge.batterysaver;
+
+import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.Mockito.atLeastOnce;
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
+import androidx.preference.PreferenceScreen;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.robolectric.RobolectricTestRunner;
+
+@RunWith(RobolectricTestRunner.class)
+public class BatterySaverSettingsTest {
+    BatterySaverSettings mFragment;
+    @Mock
+    PreferenceScreen mScreen;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+
+        mFragment = spy(new BatterySaverSettings());
+        doReturn(mScreen).when(mFragment).getPreferenceScreen();
+    }
+
+
+    @Test
+    public void setupFooter_linkAddedWhenAppropriate() {
+        doReturn("").when(mFragment).getText(anyInt());
+        doReturn("").when(mFragment).getString(anyInt());
+        mFragment.setupFooter();
+        verify(mFragment, never()).addHelpLink();
+
+        doReturn("testString").when(mFragment).getText(anyInt());
+        doReturn("testString").when(mFragment).getString(anyInt());
+        mFragment.setupFooter();
+        verify(mFragment, atLeastOnce()).addHelpLink();
+    }
+}