Added MediaProvider tests (#386)

* Media provider tests

* Moved classes to separate files

* Moved image file

* Removed unused image file

* Rebase and refactor.

Replace removed error type.
Refactor XYZMock to MockXYZ.

Co-authored-by: Doug <douglase@element.io>

UnitTests/Sources/MediaProvider/MockBackgroundTaskService.swift

@@ -0,0 +1,23 @@
+//
+// Copyright 2022 New Vector Ltd
+//
+// 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.
+//
+@testable import ElementX
+import Foundation
+
+class MockBackgroundTaskService: BackgroundTaskServiceProtocol {
+    func startBackgroundTask(withName name: String, isReusable: Bool, expirationHandler: (() -> Void)?) -> ElementX.BackgroundTaskProtocol? {
+        nil
+    }
+}