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/MockFileCache.swift

@@ -0,0 +1,52 @@
+//
+// 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
+
+enum MockFileCacheError: Error {
+    case someError
+}
+
+class MockFileCache: FileCacheProtocol {
+    var fileKey: String?
+    var fileExtension: String?
+    var fileURLToReturn: URL?
+    var storedData: Data?
+    var storedFileExtension: String?
+    var storedFileKey: String?
+    var storeURLToReturn: URL?
+    
+    func file(forKey key: String, fileExtension: String) -> URL? {
+        fileKey = key
+        self.fileExtension = fileExtension
+        return fileURLToReturn
+    }
+    
+    func store(_ data: Data, with fileExtension: String, forKey key: String) throws -> URL {
+        storedData = data
+        storedFileExtension = fileExtension
+        storedFileKey = key
+        if let storeURLToReturn {
+            return storeURLToReturn
+        } else {
+            throw MockFileCacheError.someError
+        }
+    }
+    
+    func remove(forKey key: String, fileExtension: String) throws { }
+    
+    func removeAll() throws { }
+}