Add a simple screen SwiftUI template.

RiotSwiftUI/Modules/Template/SimpleScreenExample/Test/Unit/TemplateSimpleScreenViewModelTests.swift

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+// 
+// Copyright 2021 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.
+//
+
+import XCTest
+
+@testable import RiotSwiftUI
+
+@available(iOS 14.0, *)
+class TemplateSimpleScreenViewModelTests: XCTestCase {
+    private enum Constants {
+        static let counterInitialValue = 0
+    }
+    
+    var viewModel: TemplateSimpleScreenViewModelProtocol!
+    var context: TemplateSimpleScreenViewModelType.Context!
+    
+    override func setUpWithError() throws {
+        viewModel = TemplateSimpleScreenViewModel(promptType: .regular, initialCount: Constants.counterInitialValue)
+        context = viewModel.context
+    }
+
+    func testInitialState() {
+        XCTAssertEqual(context.viewState.count, Constants.counterInitialValue)
+    }
+
+    func testCounter() throws {
+        context.send(viewAction: .incrementCount)
+        XCTAssertEqual(context.viewState.count, 1)
+        
+        context.send(viewAction: .incrementCount)
+        XCTAssertEqual(context.viewState.count, 2)
+        
+        context.send(viewAction: .decrementCount)
+        XCTAssertEqual(context.viewState.count, 1)
+    }
+}