Implemented the "asString" computed property for the TimeInterval+Computed extension in the library target.

Sources/MarvelService/Internal/Extensions/TimeInterval+Computed.swift

@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===
+//
+// This source file is part of the MarvelService open source project
+//
+// Copyright (c) -2025 Röck+Cöde VoF. and the MarvelService project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of MarvelService project authors
+//
+//===----------------------------------------------------------------------===
+
+import struct Foundation.TimeInterval
+
+extension TimeInterval {
+    
+    // MARK: Functions
+    
+    /// Converts a time interval to a string value.
+    /// - Returns: A time interval as a string.
+    var asString: String {
+        .init(format: "%f", self)
+    }
+    
+}

Tests/MarvelService/Cases/Internal/Extensions/TimeInterval+ComputedTests.swift

@@ -0,0 +1,90 @@
+//===----------------------------------------------------------------------===
+//
+// This source file is part of the MarvelService open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the MarvelService project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of MarvelService project authors
+//
+//===----------------------------------------------------------------------===
+
+import Testing
+
+import struct Foundation.TimeInterval
+
+@testable import MarvelService
+
+@Suite("Time Interval computed properties", .tags(.extension))
+struct TimeIntervalComputedTests {
+    
+    // MARK: Properties tests
+    
+#if swift(>=6.2)
+    @Test(arguments: zip(
+        Input.timestamps,
+        Output.timestampAsString
+    ))
+    func `asString`(
+        timestamp: TimeInterval,
+        expects string: String
+    ) {
+        assertAsString(
+            timestamp: timestamp,
+            expects: string
+        )
+    }
+#else
+    @Test("asString", arguments: zip(
+        Input.timestamps,
+        Output.timestampAsString
+    ))
+    func asString(
+        timestamp: TimeInterval,
+        expects string: String
+    ) {
+        assertAsString(
+            timestamp: timestamp,
+            expects: string
+        )
+    }
+#endif
+    
+}
+
+// MARK: - Assertions
+
+private extension TimeIntervalComputedTests {
+    
+    // MARK: Functions
+    
+    /// Asserts the timestamp to string conversion.
+    /// - Parameters:
+    ///   - timestamp: A timestamp to convert.
+    ///   - string: An expected timestamp converted to string.
+    func assertAsString(
+        timestamp: TimeInterval,
+        expects string: String
+    ) {
+        // GIVEN
+        // WHEN
+        let result = timestamp.asString
+        
+        // THEN
+        #expect(result == string)
+    }
+
+}
+
+// MARK: - Constants
+
+private extension Output {
+    /// A list of outcomes that are expected from converting timestamps to string.
+    static let timestampAsString: [String] = [
+        "0.000000",
+        "1000.000000",
+        "1000000.000000",
+        "1000000000.000000"
+    ]
+}

Tests/MarvelService/Types/Extensions/Tag+Customs.swift

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+//===----------------------------------------------------------------------===
+//
+// This source file is part of the MarvelService open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the MarvelService project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of MarvelService project authors
+//
+//===----------------------------------------------------------------------===
+
+import Testing
+
+extension Tag {
+    
+    // MARK: Constants
+    
+    /// A flag that indicates tests for a type extension.
+    @Tag static var `extension`: Self
+}

Tests/MarvelService/Types/Samples/Input.swift

@@ -0,0 +1,28 @@
+//===----------------------------------------------------------------------===
+//
+// This source file is part of the MarvelService open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the MarvelService project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of MarvelService project authors
+//
+//===----------------------------------------------------------------------===
+
+import struct Foundation.Date
+import struct Foundation.TimeInterval
+
+/// A namespace assigned for input arguments on test cases.
+enum Input {
+    
+    // MARK: Constants
+
+    /// A list of timestamps samples.
+    static let timestamps: [TimeInterval] = [
+        Date(timeIntervalSince1970: 0).timeIntervalSince1970,
+        Date(timeIntervalSince1970: 1_000).timeIntervalSince1970,
+        Date(timeIntervalSince1970: 1_000_000).timeIntervalSince1970,
+        Date(timeIntervalSince1970: 1_000_000_000).timeIntervalSince1970,
+    ]
+}

Tests/MarvelService/Types/Samples/Output.swift

@@ -0,0 +1,14 @@
+//===----------------------------------------------------------------------===
+//
+// This source file is part of the MarvelService open source project
+//
+// Copyright (c) 2025 Röck+Cöde VoF. and the MarvelService project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE for license information
+// See CONTRIBUTORS for the list of MarvelService project authors
+//
+//===----------------------------------------------------------------------===
+
+/// A namespace assigned for output arguments on test cases, that are expected results.
+enum Output {}