Implemented the TemplateService service in the library target.

Test/Sources/Helpers/Mocks/TemplateServiceMock.swift

@@ -0,0 +1,75 @@
+import ColibriLibrary
+import Foundation
+
+final class TemplateServiceMock {
+    
+    // MARK: Properties
+    
+    private var actions: [Action] = []
+    
+    private weak var spy: TemplateServiceSpy?
+    
+    // MARK: Initialisers
+    
+    init(
+        action: Action,
+        spy: TemplateServiceSpy? = nil
+    ) {
+        self.actions.append(action)
+        self.spy = spy
+    }
+    
+}
+
+// MARK: - TemplateServicing
+
+extension TemplateServiceMock: TemplateServicing {
+    
+    // MARK: Functions
+    
+    @discardableResult
+    func render(_ object: Any, on template: String) async throws(TemplateServiceError) -> String {
+        guard let nextAction else { return .empty }
+        
+        switch nextAction {
+        case .error(let error):
+            throw error
+        case .render(let content):
+            try await spy?.render(object, on: template)
+            return content
+        }
+    }
+    
+}
+
+// MARK: - Helpers
+
+private extension TemplateServiceMock {
+    
+    // MARK: Computed
+    
+    var nextAction: Action? {
+        guard !actions.isEmpty else {
+            return nil
+        }
+        
+        return actions.removeFirst()
+    }
+    
+}
+
+
+// MARK: - Actions
+
+extension TemplateServiceMock {
+    enum Action {
+        case error(TemplateServiceError)
+        case render(String)
+    }
+}
+
+// MARK: - String+Constants
+
+private extension String {
+    static let empty = ""
+}