Fix empty summary when no theme is set.

When current theme is empty or null, set the summary to Default.

Change-Id: I1ede31952a09956a805e6ef09c0967ecdfa5051a
Fix: 34975969
Test: make RunSettingsRoboTests

tests/robotests/src/com/android/settings/display/ThemePreferenceControllerTest.java

@@ -0,0 +1,73 @@
+/*
+ * 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 com.android.settings.display;
+
+import android.content.Context;
+import android.support.v7.preference.ListPreference;
+import com.android.settings.R;
+import com.android.settings.SettingsRobolectricTestRunner;
+import com.android.settings.TestConfig;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.robolectric.annotation.Config;
+
+import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
+@RunWith(SettingsRobolectricTestRunner.class)
+@Config(manifest = TestConfig.MANIFEST_PATH, sdk = TestConfig.SDK_VERSION)
+public class ThemePreferenceControllerTest {
+
+    @Mock
+    private ListPreference mPreference;
+    @Mock
+    private Context mContext;
+
+    private ThemePreferenceController mController;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+        mController = spy(new ThemePreferenceController(mContext));
+    }
+
+    @Test
+    public void updateState_nullTheme_shouldSetSummaryToDefault() {
+        final String[] themes = {"Theme1", "Theme2"};
+        doReturn(null).when(mController).getCurrentTheme();
+        doReturn(themes).when(mController).getAvailableThemes();
+
+        mController.updateState(mPreference);
+
+        verify(mPreference).setSummary(mContext.getString(R.string.default_theme));
+    }
+
+    @Test
+    public void updateState_themeSet_shouldSetPreferenceValue() {
+        final String[] themes = {"Theme1", "Theme2"};
+        doReturn("Theme1").when(mController).getCurrentTheme();
+        doReturn(themes).when(mController).getAvailableThemes();
+
+        mController.updateState(mPreference);
+
+        verify(mPreference).setValue("Theme1");
+    }
+}