make DBHelper follow the Java Singleton pattern

It was already behaving like a singleton, but the code was spread around in
other classes.  DBHelper does not use a private constructor though since
the tests prevent it.

app/src/main/java/org/fdroid/fdroid/Preferences.java

@@ -453,8 +453,9 @@ public final class Preferences implements SharedPreferences.OnSharedPreferenceCh
      * While it is likely that most places asking for preferences have access to a {@link Context},
      * it is a minor convenience to be able to ask for preferences without.
      */
-    public static void clearSingletonForTesting() {
+    public static void setupForTests(Context context) {
         instance = null;
+        setup(context);
     }
 
     /**

app/src/main/java/org/fdroid/fdroid/data/DBHelper.java

@@ -47,13 +47,20 @@ import org.fdroid.fdroid.data.Schema.RepoTable;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * This is basically a singleton used to represent the database at the core
+ * of all of the {@link android.content.ContentProvider}s used at the core
+ * of this app.  {@link DBHelper} is not {@code private} so that it can be easily
+ * used in test subclasses.
+ */
 @SuppressWarnings("LineLength")
-class DBHelper extends SQLiteOpenHelper {
+public class DBHelper extends SQLiteOpenHelper {
 
     private static final String TAG = "DBHelper";
 
     public static final int REPO_XML_ARG_COUNT = 8;
 
+    private static DBHelper instance;
     private static final String DATABASE_NAME = "fdroid";
 
     private static final String CREATE_TABLE_PACKAGE = "CREATE TABLE " + PackageTable.NAME
@@ -214,7 +221,22 @@ class DBHelper extends SQLiteOpenHelper {
 
     DBHelper(Context context) {
         super(context, DATABASE_NAME, null, DB_VERSION);
-        this.context = context;
+        this.context = context.getApplicationContext();
+    }
+
+    /**
+     * Only used for testing. Not quite sure how to mock a singleton variable like this.
+     */
+    public static void clearDbHelperSingleton() {
+        instance = null;
+    }
+
+    static synchronized DBHelper getInstance(Context context) {
+        if (instance == null) {
+            Utils.debugLog(TAG, "First time accessing database, creating new helper");
+            instance = new DBHelper(context);
+        }
+        return instance;
     }
 
     @Override

app/src/main/java/org/fdroid/fdroid/data/FDroidProvider.java

@@ -5,16 +5,13 @@ import android.content.ContentProvider;
 import android.content.ContentProviderOperation;
 import android.content.ContentProviderResult;
 import android.content.ContentValues;
-import android.content.Context;
 import android.content.OperationApplicationException;
 import android.content.UriMatcher;
 import android.database.sqlite.SQLiteDatabase;
 import android.net.Uri;
 import android.os.Build;
 import android.support.annotation.NonNull;
-
 import org.fdroid.fdroid.BuildConfig;
-import org.fdroid.fdroid.Utils;
 
 import java.util.ArrayList;
 import java.util.HashSet;
@@ -23,15 +20,13 @@ import java.util.Set;
 
 public abstract class FDroidProvider extends ContentProvider {
 
-    private static final String TAG = "FDroidProvider";
+    public static final String TAG = "FDroidProvider";
 
     static final String AUTHORITY = BuildConfig.APPLICATION_ID + ".data";
 
     static final int CODE_LIST = 1;
     static final int CODE_SINGLE = 2;
 
-    private static DBHelper dbHelper;
-
     private boolean isApplyingBatch;
 
     protected abstract String getTableName();
@@ -73,28 +68,13 @@ public abstract class FDroidProvider extends ContentProvider {
         return result;
     }
 
-    /**
-     * Only used for testing. Not quite sure how to mock a singleton variable like this.
-     */
-    public static void clearDbHelperSingleton() {
-        dbHelper = null;
-    }
-
-    private static synchronized DBHelper getOrCreateDb(Context context) {
-        if (dbHelper == null) {
-            Utils.debugLog(TAG, "First time accessing database, creating new helper");
-            dbHelper = new DBHelper(context);
-        }
-        return dbHelper;
-    }
-
     @Override
     public boolean onCreate() {
         return true;
     }
 
     protected final synchronized SQLiteDatabase db() {
-        return getOrCreateDb(getContext().getApplicationContext()).getWritableDatabase();
+        return DBHelper.getInstance(getContext()).getWritableDatabase();
     }
 
     @Override

app/src/test/java/org/fdroid/fdroid/AntiFeaturesTest.java

@@ -2,7 +2,6 @@ package org.fdroid.fdroid;
 
 import android.app.Application;
 import android.content.ContentValues;
-
 import org.fdroid.fdroid.data.Apk;
 import org.fdroid.fdroid.data.ApkProvider;
 import org.fdroid.fdroid.data.App;
@@ -12,7 +11,6 @@ import org.fdroid.fdroid.data.AppProvider;
 import org.fdroid.fdroid.data.FDroidProviderTest;
 import org.fdroid.fdroid.data.InstalledAppTestUtils;
 import org.fdroid.fdroid.data.Schema;
-import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -21,9 +19,9 @@ import org.robolectric.annotation.Config;
 
 import java.util.List;
 
-import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 
 @Config(constants = BuildConfig.class, application = Application.class, sdk = 24)
 @RunWith(RobolectricTestRunner.class)
@@ -35,7 +33,7 @@ public class AntiFeaturesTest extends FDroidProviderTest {
 
     @Before
     public void setup() {
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
 
         ContentValues vulnValues = new ContentValues(1);
         vulnValues.put(Schema.ApkTable.Cols.AntiFeatures.ANTI_FEATURES, "KnownVuln,ContainsGreenButtons");
@@ -58,11 +56,6 @@ public class AntiFeaturesTest extends FDroidProviderTest {
         AppProvider.Helper.recalculatePreferredMetadata(context);
     }
 
-    @After
-    public void tearDown() {
-        Preferences.clearSingletonForTesting();
-    }
-
     private static String generateHash(String packageName, int versionCode) {
         return packageName + "-" + versionCode;
     }

app/src/test/java/org/fdroid/fdroid/data/AppPrefsProviderTest.java

@@ -1,7 +1,6 @@
 package org.fdroid.fdroid.data;
 
 import android.app.Application;
-
 import org.fdroid.fdroid.Assert;
 import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.TestUtils;
@@ -11,10 +10,10 @@ import org.junit.runner.RunWith;
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.annotation.Config;
 
-import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertTrue;
 
 @Config(constants = BuildConfig.class, application = Application.class, sdk = 24)
 @RunWith(RobolectricTestRunner.class)

app/src/test/java/org/fdroid/fdroid/data/AppProviderTest.java

@@ -10,7 +10,6 @@ import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.Preferences;
 import org.fdroid.fdroid.TestUtils;
 import org.fdroid.fdroid.data.Schema.AppMetadataTable.Cols;
-import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -40,12 +39,7 @@ public class AppProviderTest extends FDroidProviderTest {
     @Before
     public void setup() {
         TestUtils.registerContentProvider(AppProvider.getAuthority(), AppProvider.class);
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
-    }
-
-    @After
-    public void tearDown() {
-        Preferences.clearSingletonForTesting();
     }
 
     /**

app/src/test/java/org/fdroid/fdroid/data/FDroidProviderTest.java

@@ -1,7 +1,6 @@
 package org.fdroid.fdroid.data;
 
 import android.content.ContextWrapper;
-
 import org.fdroid.fdroid.TestUtils;
 import org.junit.After;
 import org.junit.Before;
@@ -24,7 +23,7 @@ public abstract class FDroidProviderTest {
     @After
     public final void tearDownBase() {
         CategoryProvider.Helper.clearCategoryIdCache();
-        FDroidProvider.clearDbHelperSingleton();
+        DBHelper.clearDbHelperSingleton();
     }
 
 }

app/src/test/java/org/fdroid/fdroid/data/InstalledAppProviderTest.java

@@ -8,7 +8,6 @@ import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.Preferences;
 import org.fdroid.fdroid.TestUtils;
 import org.fdroid.fdroid.data.Schema.InstalledAppTable.Cols;
-import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -31,12 +30,7 @@ public class InstalledAppProviderTest extends FDroidProviderTest {
     @Before
     public void setup() {
         TestUtils.registerContentProvider(InstalledAppProvider.getAuthority(), InstalledAppProvider.class);
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
-    }
-
-    @After
-    public void tearDown() {
-        Preferences.clearSingletonForTesting();
     }
 
     @Test

app/src/test/java/org/fdroid/fdroid/data/PreferredSignatureTest.java

@@ -2,11 +2,9 @@ package org.fdroid.fdroid.data;
 
 import android.app.Application;
 import android.content.Context;
-
 import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.Preferences;
 import org.fdroid.fdroid.TestUtils;
-import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -24,7 +22,7 @@ public class PreferredSignatureTest extends FDroidProviderTest {
     @Before
     public void setup() {
         TestUtils.registerContentProvider(AppProvider.getAuthority(), AppProvider.class);
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
 
         // This is what the FDroidApp does when this preference is changed. Need to also do this under testing.
         Preferences.get().registerUnstableUpdatesChangeListener(new Preferences.ChangeListener() {
@@ -35,11 +33,6 @@ public class PreferredSignatureTest extends FDroidProviderTest {
         });
     }
 
-    @After
-    public void tearDown() {
-        Preferences.clearSingletonForTesting();
-    }
-
     private Repo createFDroidRepo() {
         return RepoProviderTest.insertRepo(context, "https://f-droid.org/fdroid/repo", "", "", "");
     }

app/src/test/java/org/fdroid/fdroid/data/ProviderUriTests.java

@@ -39,7 +39,7 @@ public class ProviderUriTests {
 
     @After
     public void teardown() {
-        FDroidProvider.clearDbHelperSingleton();
+        DBHelper.clearDbHelperSingleton();
     }
 
     @Test

app/src/test/java/org/fdroid/fdroid/data/RepoProviderTest.java

@@ -26,7 +26,6 @@ import android.content.ContentValues;
 import android.content.Context;
 import android.net.Uri;
 import android.support.annotation.Nullable;
-
 import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.R;
 import org.fdroid.fdroid.Utils;

app/src/test/java/org/fdroid/fdroid/data/SuggestedVersionTest.java

@@ -5,7 +5,6 @@ import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.Preferences;
 import org.fdroid.fdroid.TestUtils;
 import org.fdroid.fdroid.data.Schema.AppMetadataTable.Cols;
-import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -24,7 +23,7 @@ public class SuggestedVersionTest extends FDroidProviderTest {
     @Before
     public void setup() {
         TestUtils.registerContentProvider(AppProvider.getAuthority(), AppProvider.class);
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
 
         // This is what the FDroidApp does when this preference is changed. Need to also do this under testing.
         Preferences.get().registerUnstableUpdatesChangeListener(new Preferences.ChangeListener() {
@@ -35,11 +34,6 @@ public class SuggestedVersionTest extends FDroidProviderTest {
         });
     }
 
-    @After
-    public void tearDown() {
-        Preferences.clearSingletonForTesting();
-    }
-
     @Test
     public void singleRepoSingleSig() {
         App singleApp = TestUtils.insertApp(

app/src/test/java/org/fdroid/fdroid/updater/AcceptableMultiRepoUpdaterTest.java

@@ -4,7 +4,6 @@ package org.fdroid.fdroid.updater;
 import android.content.ContentValues;
 import android.support.annotation.NonNull;
 import android.util.Log;
-
 import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.RepoUpdater.UpdateException;
 import org.fdroid.fdroid.data.Repo;

app/src/test/java/org/fdroid/fdroid/updater/IndexV1UpdaterTest.java

@@ -26,7 +26,6 @@ import org.fdroid.fdroid.data.Repo;
 import org.fdroid.fdroid.data.RepoProvider;
 import org.fdroid.fdroid.data.RepoPushRequest;
 import org.fdroid.fdroid.mock.RepoDetails;
-import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -66,12 +65,7 @@ public class IndexV1UpdaterTest extends FDroidProviderTest {
 
     @Before
     public void setup() {
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
-    }
-
-    @After
-    public void tearDown() {
-        Preferences.clearSingletonForTesting();
     }
 
     @Test

app/src/test/java/org/fdroid/fdroid/updater/Issue763MultiRepo.java

@@ -1,7 +1,6 @@
 package org.fdroid.fdroid.updater;
 
 import android.content.ContentValues;
-
 import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.RepoUpdater;
 import org.fdroid.fdroid.data.Apk;

app/src/test/java/org/fdroid/fdroid/updater/MultiRepoUpdaterTest.java

@@ -17,7 +17,6 @@ import org.fdroid.fdroid.data.FDroidProviderTest;
 import org.fdroid.fdroid.data.Repo;
 import org.fdroid.fdroid.data.RepoProvider;
 import org.fdroid.fdroid.data.Schema;
-import org.junit.After;
 import org.junit.Before;
 
 import java.io.File;
@@ -86,12 +85,7 @@ public abstract class MultiRepoUpdaterTest extends FDroidProviderTest {
         RepoProvider.Helper.remove(context, 3);
         RepoProvider.Helper.remove(context, 4);
 
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
-    }
-
-    @After
-    public final void tearDownMultiRepo() {
-        Preferences.clearSingletonForTesting();
     }
 
     protected void assertApp(String packageName, int[] versionCodes) {

app/src/test/java/org/fdroid/fdroid/updater/ProperMultiRepoUpdaterTest.java

@@ -4,7 +4,6 @@ package org.fdroid.fdroid.updater;
 import android.content.ContentValues;
 import android.support.annotation.StringDef;
 import android.util.Log;
-
 import org.fdroid.fdroid.BuildConfig;
 import org.fdroid.fdroid.RepoUpdater;
 import org.fdroid.fdroid.TestUtils;

app/src/test/java/org/fdroid/fdroid/views/AppDetailsAdapterTest.java

@@ -14,7 +14,7 @@ import org.fdroid.fdroid.R;
 import org.fdroid.fdroid.data.Apk;
 import org.fdroid.fdroid.data.App;
 import org.fdroid.fdroid.data.AppProviderTest;
-import org.fdroid.fdroid.data.FDroidProvider;
+import org.fdroid.fdroid.data.DBHelper;
 import org.fdroid.fdroid.data.FDroidProviderTest;
 import org.fdroid.fdroid.data.Repo;
 import org.fdroid.fdroid.data.RepoProviderTest;
@@ -36,7 +36,7 @@ public class AppDetailsAdapterTest extends FDroidProviderTest {
     @Before
     public void setup() {
         ImageLoader.getInstance().init(ImageLoaderConfiguration.createDefault(context));
-        Preferences.setup(context);
+        Preferences.setupForTests(context);
 
         Repo repo = RepoProviderTest.insertRepo(context, "http://www.example.com/fdroid/repo", "", "", "Test Repo");
         app = AppProviderTest.insertApp(contentResolver, context, "com.example.app", "Test App",
@@ -46,8 +46,7 @@ public class AppDetailsAdapterTest extends FDroidProviderTest {
     @After
     public void teardown() {
         ImageLoader.getInstance().destroy();
-        FDroidProvider.clearDbHelperSingleton();
+        DBHelper.clearDbHelperSingleton();
-        Preferences.clearSingletonForTesting();
     }
 
     @Test