Parallelize Unit Tests in Your iOS App

Apr 24 2025 · Fastlane - from zero to hero

Introduction

In this post, I’ll show you two ways to run unit tests in your iOS app: using the Xcode CLI with Bash and using Fastlane. Both approaches have their pros and cons, and you can choose the one that best fits your workflow. Whether you’re working in a CI/CD environment or running tests locally, these methods will help you automate your testing process.

Prerequisites

For both methods, you’ll need:

• Xcode installed
• A working iOS app with unit tests

For the Fastlane method, you’ll also need:

• Fastlane installed

Method 1: Using Xcode CLI and Bash

This method uses the Xcode CLI (xcodebuild) and a Bash script to run your tests. It’s lightweight and doesn’t require any third-party tools.

Script

Here’s the script to run your unit tests:

#!/bin/bash

set -u  # Treat unset variables as errors

# Configurable variables
SCHEME="YourSchemeName"
DESTINATION="platform=iOS Simulator,name=iPhone 16 Pro,OS=latest"
PROJECT="YourProject.xcodeproj"

# Run tests and capture exit code
set -o pipefail
xcodebuild \
-scheme "$SCHEME" \
-project "$PROJECT" \
-destination "$DESTINATION" \
-parallel-testing-enabled YES \
-parallel-testing-worker-count 4 \
clean test | tee xcodebuild.log | xcpretty

EXIT_CODE=${PIPESTATUS[0]}

if [ "$EXIT_CODE" -ne 0 ]; then
    echo "❌ Unit tests failed!"
    exit "$EXIT_CODE"
else
    echo "✅ All unit tests passed!"
fi

Running the Script

Save the script to a file (e.g., run_tests.sh), make it executable, and run it:

chmod +x run_tests.sh
./run_tests.sh

This will run your tests and display the results in the terminal.

Method 2: Using Fastlane

Fastlane is a popular tool for automating iOS and Android development tasks. It provides a simple way to run tests and integrates well with CI/CD pipelines.

Setting Up Fastlane

1. Install Fastlane:

   brew install fastlane
   

2. Navigate to your project directory and initialize Fastlane:

   fastlane init
   

   Follow the prompts to set up Fastlane for your project.

Adding a Test Lane

Edit your Fastfile to add a lane for running tests:

default_platform(:ios)

platform :ios do
  desc "Run unit tests"
  lane :run_tests do
    scan(
      scheme: "YourSchemeName",
      devices: ["iPhone 16 Pro"],
      clean: true,
      parallel_testing: true,
      concurrent_workers: 4,
      output_directory: "./fastlane/test_output",
      output_types: "html,junit"
    )
  end
end

Running the Test Lane

Run the test lane using the following command:

fastlane run_tests

Fastlane will execute your tests and generate a report in the ./fastlane/test_output directory.

Comparison: Xcode CLI vs. Fastlane

Conclusion

Both methods are effective for running unit tests in your iOS app. If you prefer a lightweight, script-based approach, the Xcode CLI with Bash is a great choice. If you want a more feature-rich solution with built-in reporting and CI/CD integration, Fastlane is the way to go.

Try both methods and see which one works best for your workflow. Let me know if you have any questions or need help setting up either approach. Happy testing!