Fix unit tests to work with a singleton DBHelper instance.

The fix for the database locking bug was to have a singleton
`DBHelper` instance. This breaks tests because multiple tests
share the same database. The solution is to:

 * Hack together a static method which clears the singleton,
   then invoke it in the `setUp()` method for relevant test cases.

 * Ensure the mock context provided to the providers during
   the tests is able to provide a context via `getApplicationContext()`.
   Without this, the mock context throws an `UnsupportedOperationException`
   when invoking this method.

F-Droid/src/org/fdroid/fdroid/data/FDroidProvider.java

@@ -72,6 +72,13 @@ 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");

F-Droid/test/src/android/test/ProviderTestCase2MockContext.java

@@ -20,6 +20,7 @@ import android.annotation.TargetApi;
 import android.content.ContentProvider;
 import android.content.ContentResolver;
 import android.content.Context;
+import android.content.ContextWrapper;
 import android.content.res.Resources;
 import android.database.DatabaseUtils;
 import android.os.Build;
@@ -136,12 +137,20 @@ public abstract class ProviderTestCase2MockContext<T extends ContentProvider> ex
 
         mResolver = new MockContentResolver();
         final String filenamePrefix = "test.";
-        RenamingDelegatingContext targetContextWrapper = new
+        final RenamingDelegatingContext targetContextWrapper = new
                 RenamingDelegatingContext(
                 createMockContext(new MockContext2()), // The context that most methods are delegated to
                 getContext(), // The context that file methods are delegated to
                 filenamePrefix);
-        mProviderContext = new IsolatedContext(mResolver, targetContextWrapper);
+
+        mProviderContext = new IsolatedContext(mResolver, new ContextWrapper(targetContextWrapper) {
+            // The FDroidProvider class needs access to an application context in order to initialize
+            // the singleton DBHelper instance.
+            @Override
+            public Context getApplicationContext() {
+                return targetContextWrapper;
+            }
+        });
 
         mProvider = mProviderClass.newInstance();
         mProvider.attachInfo(mProviderContext, null);

F-Droid/test/src/mock/MockContextSwappableComponents.java

@@ -1,5 +1,6 @@
 package mock;
 
+import android.content.Context;
 import android.content.pm.PackageManager;
 import android.content.res.Resources;
 import android.test.mock.MockContentResolver;
@@ -8,7 +9,6 @@ import android.test.mock.MockContext;
 public class MockContextSwappableComponents extends MockContext {
 
     private PackageManager packageManager;
-
     private Resources resources;
     private MockContentResolver contentResolver;
 

F-Droid/test/src/org/fdroid/fdroid/FDroidProviderTest.java

@@ -45,6 +45,8 @@ public abstract class FDroidProviderTest<T extends FDroidProvider> extends Provi
     public void setUp() throws Exception {
         super.setUp();
 
+        FDroidProvider.clearDbHelperSingleton();
+
         // Instantiate all providers other than the one which was already created by the base class.
         // This is because F-Droid providers tend to perform joins onto tables managed by other
         // providers, and so we need to be able to insert into those other providers for these

F-Droid/test/src/org/fdroid/fdroid/MultiRepoUpdaterTest.java

@@ -18,6 +18,7 @@ import org.fdroid.fdroid.RepoUpdater.UpdateException;
 import org.fdroid.fdroid.data.Apk;
 import org.fdroid.fdroid.data.ApkProvider;
 import org.fdroid.fdroid.data.AppProvider;
+import org.fdroid.fdroid.data.FDroidProvider;
 import org.fdroid.fdroid.data.Repo;
 import org.fdroid.fdroid.data.RepoProvider;
 import org.fdroid.fdroid.data.TempApkProvider;
@@ -122,12 +123,20 @@ public class MultiRepoUpdaterTest extends InstrumentationTestCase {
         public File getDatabasePath(String name) {
             return new File(getInstrumentation().getContext().getFilesDir(), "fdroid_test.db");
         }
+
+        @Override
+        public Context getApplicationContext() {
+            // Used by the DBHelper singleton instance.
+            return this;
+        }
     }
 
     @Override
     public void setUp() throws Exception {
         super.setUp();
 
+        FDroidProvider.clearDbHelperSingleton();
+
         context = new TestContext();
 
         testFilesDir = TestUtils.getWriteableDir(getInstrumentation());