add unit tests

test/random_service_test.dart

@@ -0,0 +1,17 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:odin/services/random_service.dart';
+
+void main() {
+  group("Random -", () {
+    test("Result should be String", () {
+      final RandomService _randomService = RandomService();
+      final String randomText = _randomService.getRandomString(10);
+      expect(randomText, isA<String>());
+    });
+    test("Result should be 10 char long", () {
+      final RandomService _randomService = RandomService();
+      final String randomText = _randomService.getRandomString(10);
+      expect(randomText, hasLength(10));
+    });
+  });
+}

test/shortner_service_test.dart

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+import 'package:flutter_test/flutter_test.dart';
+import 'package:odin/services/shortener_service.dart';
+
+void main() {
+  group("Shortener -", () {
+    test("Url should contain shrtco.de", () async {
+      final ShortenerService _shortnerService = ShortenerService();
+      const String url = "https://www.google.com";
+      final String? shortUrl = await _shortnerService.getShortUrl(url: url);
+      expect(shortUrl, stringContainsInOrder(["https://", "shrtco.de"]));
+    });
+  });
+}

test/zip_service_test.dart

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+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:odin/services/locator.dart';
+import 'package:odin/services/zip_service.dart';
+import 'package:path/path.dart';
+import 'package:path_provider/path_provider.dart';
+
+void main() {
+  setUpAll(() => setupLocator());
+  group("Zip -", () {
+    test("Result should be a File", () async {
+      final ZipService _zipService = ZipService();
+      final directory = await getTemporaryDirectory();
+      final file = File('${directory.path}\\hello.txt');
+      file.writeAsStringSync('Hello World!');
+      final File zippedFile = await _zipService.zipFile(fileToZips: [file]);
+      expect(zippedFile, isA<File>());
+    });
+    test("Result should be of zip extension", () async {
+      final ZipService _zipService = ZipService();
+      final directory = await getTemporaryDirectory();
+      final file = File('${directory.path}\\hello2.txt');
+      file.writeAsStringSync('Hello World!');
+      final File zippedFile = await _zipService.zipFile(fileToZips: [file]);
+      expect(basename(zippedFile.path), stringContainsInOrder([".zip"]));
+    });
+    test("Result should contain first file name", () async {
+      final ZipService _zipService = ZipService();
+      final directory = await getTemporaryDirectory();
+      final file = File('${directory.path}\\hello3.txt');
+      file.writeAsStringSync('Hello World!');
+      final file2 = File('${directory.path}\\hello4.txt');
+      file2.writeAsStringSync('Hello World!');
+      final File zippedFile =
+          await _zipService.zipFile(fileToZips: [file, file2]);
+      expect(basename(zippedFile.path),
+          stringContainsInOrder(["hello3", "txt", ".zip"]));
+    });
+  });
+}