Implemented the initialization functions for the DocCMiddleware type in the library target.

Sources/DocCMiddleware/Public/Middlewares/DocCMiddleware.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import Hummingbird
+
+import class NIOPosix.NIOThreadPool
+import struct Logging.Logger
+
+/// A middleware that proxies requests to `DocC` documentation containers within a hosting app.
+public struct DocCMiddleware {
+    
+    // MARK: Properties
+    
+    /// A protocol that defines file system interactions.
+    let fileProvider: any FileProvider
+    
+    /// A type that interacts with the logging system.
+    let logger: Logger
+    
+    // MARK: Initializers
+    
+    /// Initializes this middleware with the root path to the `DocC` documentation containers in the file system.
+    /// - Parameters:
+    ///   - pathToRoot: A path to the root folder in which the `DocC` documentation container are located.
+    ///   - logger: A type that interacts with the logging system.
+    ///   - threadPool: A representation of the thread pool that should be used in case some blocking work needs to be performed for which no non-blocking API exists.
+    init(
+        pathToRoot rootFolder: String,
+        logger: Logger,
+        threadPool: NIOThreadPool = .singleton
+    ) {
+        self.fileProvider = LocalFileSystem(
+            rootFolder: rootFolder,
+            threadPool: threadPool,
+            logger: logger
+        )
+        self.logger = logger
+    }
+    
+    /// Initializes this middleware with a type conforming to the `FileProvider` protocol.
+    /// - Parameters:
+    ///   - fileProvider: A type that conforms to the protocol that defines file system interactions.
+    ///   - logger: A type that interacts with the logging system.
+    init(
+        fileProvider: any FileProvider,
+        logger: Logger
+    ) {
+        self.fileProvider = fileProvider
+        self.logger = logger
+    }
+    
+}

Tests/DocCMiddleware/Tests/Public/Middlewares/DocCMiddlewareTests.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import Testing
+
+import struct Hummingbird.LocalFileSystem
+import struct Logging.Logger
+import protocol Hummingbird.FileProvider
+
+@testable import DocCMiddleware
+
+@Suite("DocC Middleware")
+struct DocCMiddlewareTests {
+    
+    // MARK: Initializers tests
+
+#if swift(>=6.2)
+    @Test(.tags(.initializer))
+    func `initialize with path to root`() {
+        assertInit(pathToRoot: "/path/to/root/docc/documentation")
+    }
+    
+    @Test(.tags(.initializer))
+    func `initialize with type that conforms to the FileProvider protocol`() {
+        // GIVEN
+        assertInit(fileProvider: FileProviderStub())
+    }
+#else
+    @Test("initialize with path to root", .tags(.initializer))
+    func initWithRootPath() {
+        assertInit(pathToRoot: "/path/to/root/docc/documentation")
+    }
+    
+    @Test("initialize with type that conforms to the FileProvider protocol", .tags(.initializer))
+    func initWithFileProviderType() {
+        assertInit(fileProvider: FileProviderStub())
+    }
+#endif
+
+}
+
+// MARK: - Assertions
+
+private extension DocCMiddlewareTests {
+    
+    // MARK: Functions
+    
+    /// Asserts the initialization of a `DocCMiddleware` type with a root path in the file system.
+    /// - Parameters:
+    ///   - pathToRoot: A path to the root `DocC` documentation containers.
+    ///   - logger: A type that interacts with the logging system.
+    func assertInit(
+        pathToRoot: String,
+        logger: Logger = .test
+    ) {
+        // GIVEN
+        // WHEN
+        let middleware = DocCMiddleware(
+            pathToRoot: pathToRoot,
+            logger: logger
+        )
+        
+        // THEN
+        #expect(middleware.fileProvider is LocalFileSystem)
+        #expect(middleware.logger.label == logger.label)
+        #expect(middleware.logger.logLevel == logger.logLevel)
+    }
+    
+    /// Asserts the initialization of a `DocCMiddleware` type with a type that conforms to the `FileProvider` protocol.
+    /// - Parameters:
+    ///   - fileProvider: A type that conforms to the protocol that defines file system interactions.
+    ///   - logger: A type that interacts with the logging system.
+    func assertInit(
+        fileProvider: any FileProvider,
+        logger: Logger = .test
+    ) {
+        // GIVEN
+        // WHEN
+        let middleware = DocCMiddleware(
+            fileProvider: fileProvider,
+            logger: logger
+        )
+        
+        // THEN
+        #expect(type(of:middleware.fileProvider) == type(of: fileProvider))
+        #expect(middleware.logger.label == logger.label)
+        #expect(middleware.logger.logLevel == logger.logLevel)
+    }
+    
+}

Tests/DocCMiddleware/Types/Extensions/Logger+Constants.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import Logging
+import Testing
+
+extension Logger {
+    
+    // MARK: Constants
+    
+    /// Creates a logger instance that is ready to use in test cases.
+    static let test: Self = {
+        var logger = Logger(label: "test.hummingbird-docc-middleware.logger")
+        
+        logger.logLevel = try! #require(Logger.Level.allCases.randomElement())
+        
+        return logger
+    }()
+    
+}

Tests/DocCMiddleware/Types/Extensions/Tag+Constants.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import Testing
+
+extension Tag {
+    
+    // MARK: Constants
+    
+    /// Tag that indicate a test case for a type initialization.
+    @Tag static var initializer: Self
+    
+}

Tests/DocCMiddleware/Types/Stubs/FileProviderStub.swift

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+// ===----------------------------------------------------------------------===
+//
+// This source file is part of the Hummingbird DocC Middleware open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the Hummingbird DocC Middleware project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of Hummingbird DocC Middleware project authors
+//
+// ===----------------------------------------------------------------------===
+
+import Hummingbird
+
+/// A stub that conforms to the `FileProvider` protocol.
+struct FileProviderStub {}
+
+// MARK: - FileProvider
+
+extension FileProviderStub: FileProvider {
+    
+    // MARK: Type aliases
+    
+    typealias FileAttributes = String
+    typealias FileIdentifier = String
+    
+    // MARK: Functions
+    
+    func getFileIdentifier(_ path: String) -> String? {
+        nil
+    }
+    
+    func getAttributes(id: String) async throws -> String? {
+        nil
+    }
+    
+    func loadFile(
+        id: String,
+        context: some RequestContext
+    ) async throws -> ResponseBody {
+        .init()
+    }
+    
+    func loadFile(
+        id: String,
+        range: ClosedRange<Int>,
+        context: some RequestContext
+    ) async throws -> ResponseBody {
+        .init()
+    }
+    
+}
+