feat(stac_cli): add unit testing infrastructure and core command tests

packages/stac_cli/test/commands/cli_commands_test.dart

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+import 'package:test/test.dart';
+import 'package:args/command_runner.dart';
+import 'package:stac_cli/src/commands/build_command.dart';
+import 'package:stac_cli/src/commands/init_command.dart';
+import 'package:stac_cli/src/commands/deploy_command.dart';
+import 'package:stac_cli/src/config/env.dart';
+
+/// Test suite for verifying core Stac CLI commands.
+void main() {
+  group('CLI Commands', () {
+    late CommandRunner<int> runner;
+
+    setUp(() {
+      // Initialize environment with mock values to satisfy required checks in services.
+      // This allows testing command configuration without needing real API keys.
+      configureEnvironment({
+        'STAC_BASE_API_URL': 'https://api.test.stac.dev',
+        'STAC_GOOGLE_CLIENT_ID': 'test-client-id',
+        'STAC_FIREBASE_API_KEY': 'test-api-key',
+      });
+
+      runner = CommandRunner<int>('stac', 'Stac CLI test runner');
+      runner.addCommand(BuildCommand());
+      runner.addCommand(InitCommand());
+      runner.addCommand(DeployCommand());
+    });
+
+    test('build command has correct name and description', () {
+      final command = runner.commands['build'];
+      expect(command, isNotNull, reason: 'BuildCommand should be registered');
+      expect(command!.name, equals('build'));
+      expect(command.description, isNotEmpty);
+    });
+
+    test('init command has correct name and description', () {
+      final command = runner.commands['init'];
+      expect(command, isNotNull, reason: 'InitCommand should be registered');
+      expect(command!.name, equals('init'));
+      expect(command.description, isNotEmpty);
+    });
+
+    test('deploy command has correct name and description', () {
+      final command = runner.commands['deploy'];
+      expect(command, isNotNull, reason: 'DeployCommand should be registered');
+      expect(command!.name, equals('deploy'));
+      expect(command.description, isNotEmpty);
+    });
+  });
+}

packages/stac_cli/test/utils/file_utils_test.dart

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+import 'dart:io';
+import 'package:test/test.dart';
+import 'package:stac_cli/src/utils/file_utils.dart';
+import 'package:path/path.dart' as path;
+
+/// Test suite for Stac CLI file utility operations.
+void main() {
+  group('FileUtils', () {
+    // Basic verification of environment-dependent directory getters.
+    test('homeDirectory returns a non-empty string on this OS', () {
+      final home = FileUtils.homeDirectory;
+      expect(home, isNotEmpty);
+    });
+
+    test('configDirectory path is generated', () {
+      final config = FileUtils.configDirectory;
+      expect(config, isNotEmpty);
+    });
+
+    // Integrated test for file system operations using a temporary directory.
+    test('integrated file operations: create, read, and delete', () async {
+      // Setup a clean temporary sandbox for this test.
+      final tempDir = Directory.systemTemp.createTempSync('stac_cli_test');
+      final filePath = path.join(tempDir.path, 'test_file.txt');
+
+      try {
+        // 1. Initial State: file should not exist.
+        expect(await FileUtils.fileExists(filePath), isFalse);
+
+        // 2. Write Operation: create file with content.
+        await FileUtils.writeFile(filePath, 'hello world');
+        expect(await FileUtils.fileExists(filePath), isTrue);
+
+        // 3. Read Operation: verify content matches.
+        final content = await FileUtils.readFile(filePath);
+        expect(content, equals('hello world'));
+
+        // 4. Delete Operation: cleanup file.
+        await FileUtils.deleteFile(filePath);
+        expect(await FileUtils.fileExists(filePath), isFalse);
+      } finally {
+        // Always cleanup the temporary directory logic even if tests fail.
+        if (tempDir.existsSync()) {
+          tempDir.deleteSync(recursive: true);
+        }
+      }
+    });
+  });
+}