Implemented the DependencyService service

Tests/Dependencies/Services/DependencyServiceTests.swift

@@ -0,0 +1,57 @@
+//
+//  DependencyServiceTests.swift
+//  DependenciesTests
+//
+//  Created by Javier Cicchelli on 11/04/2023.
+//  Copyright © 2023 Röck+Cöde. All rights reserved.
+//
+
+import Dependencies
+import XCTest
+
+final class DependencyServiceTests: XCTestCase {
+
+    // MARK: Setup
+    
+    override func setUp() {
+        DependencyService[\.testService] = SomeService()
+    }
+    
+    // MARK: Tests
+
+    func test_readDependencyKey() async throws {
+        // GIVEN
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+    
+    func test_writeDependencyKey() async throws {
+        // GIVEN
+        DependencyService[\.testService] = SomeOtherService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeOtherService)
+    }
+    
+    func test_writeDependencyKeyTwice() async throws {
+        // GIVEN
+        DependencyService[\.testService] = SomeOtherService()
+        DependencyService[\.testService] = SomeService()
+        
+        // WHEN
+        let service = DependencyService[\.testService]
+        
+        // THEN
+        XCTAssertNotNil(service)
+        XCTAssert(service is SomeService)
+    }
+
+}