Add helper method to throw if command is not installed

tools/sz_repo_cli/lib/src/commands/src/format_command.dart

@@ -11,6 +11,7 @@ import 'dart:io';
 
 import 'package:sz_repo_cli/src/common/common.dart';
 import 'package:sz_repo_cli/src/common/src/run_source_of_truth_command.dart';
+import 'package:sz_repo_cli/src/common/src/throw_if_command_is_not_installed.dart';
 
 class FormatCommand extends ConcurrentCommand {
   FormatCommand(SharezoneRepo repo) : super(repo);
@@ -37,22 +38,10 @@ class FormatCommand extends ConcurrentCommand {
       await formatCode(package);
 
   Future<void> _throwIfPrettierIsNotInstalled() async {
-    if (Platform.isWindows) {
-      // We skip this check on Windows because "which -s" is not available.
-      return;
-    }
-
-    // Check if "which -s prettier" returns 0.
-    // If not, throw an exception.
-    final result = await runProcess(
-      'which',
-      ['-s', 'prettier'],
+    await throwIfCommandIsNotInstalled(
+      command: 'prettier',
+      instructionsToInstall: 'Run `npm install -g prettier` to install it.',
     );
-    if (result.exitCode != 0) {
-      throw Exception(
-        'Prettier is not installed. Run `npm install -g prettier` to install it.',
-      );
-    }
   }
 
   Future<void> _formatActionFiles({

tools/sz_repo_cli/lib/src/common/src/app_store_connect_utils.dart

@@ -12,6 +12,7 @@ import 'package:args/args.dart';
 import 'package:sz_repo_cli/src/common/src/apple_track.dart';
 import 'package:sz_repo_cli/src/common/src/run_process.dart';
 import 'package:sz_repo_cli/src/common/src/sharezone_repo.dart';
+import 'package:sz_repo_cli/src/common/src/throw_if_command_is_not_installed.dart';
 
 const privateKeyOptionName = 'private-key';
 const keyIdOptionName = 'key-id';
@@ -131,17 +132,11 @@ AppleTrack _getAppleTrack({
 }
 
 Future<void> throwIfCodemagiCliToolsAreNotInstalled() async {
-  // Check if "which -s app-store-connect" returns 0.
-  // If not, throw an exception.
-  final result = await runProcess(
-    'which',
-    ['-s', 'app-store-connect'],
+  await throwIfCommandIsNotInstalled(
+    command: 'app-store-connect',
+    instructionsToInstall:
+        'Docs to install them: https://github.com/codemagic-ci-cd/cli-tools#installing',
   );
-  if (result.exitCode != 0) {
-    throw Exception(
-      'Codemagic CLI tools are not installed. Docs to install them: https://github.com/codemagic-ci-cd/cli-tools#installing',
-    );
-  }
 }
 
 void addWhatsNewOption(ArgParser argParser) {

tools/sz_repo_cli/lib/src/common/src/throw_if_command_is_not_installed.dart

@@ -0,0 +1,42 @@
+// Copyright (c) 2023 Sharezone UG (haftungsbeschränkt)
+// Licensed under the EUPL-1.2-or-later.
+//
+// You may obtain a copy of the Licence at:
+// https://joinup.ec.europa.eu/software/page/eupl
+//
+// SPDX-License-Identifier: EUPL-1.2
+
+import 'dart:io';
+
+import 'package:sz_repo_cli/src/common/src/run_process.dart';
+
+/// Throws an exception if [command] is not installed.
+///
+/// Optionally, you can pass [instructionsToInstall] to throw an helpful
+/// exception.
+///
+/// Currently, we skip this method for [Platform.isWindows] because "which -s"
+/// is not available for Windows.
+Future<void> throwIfCommandIsNotInstalled({
+  required String command,
+  String? instructionsToInstall,
+}) async {
+  if (Platform.isWindows) {
+    // We skip on Windows the check because "which -s" is not available for
+    // Windows.
+    return;
+  }
+
+  final result = await runProcess(
+    'which',
+    ['-s', command],
+  );
+  if (result.exitCode != 0) {
+    String message = 'Command "$command" is not installed.';
+    if (instructionsToInstall != null) {
+      message += ' $instructionsToInstall';
+    }
+
+    throw Exception(message);
+  }
+}