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avito-tech/Emcee v11.0.0
Emcee is a tool that runs iOS tests in parallel using multiple simulators across many Macs
⭐️ 182
πŸ•“ 36 weeks ago
.package(url: "https://github.com/avito-tech/Emcee.git", from: "v11.0.0")

Emcee Banner

Welcome to Emcee project, an ultimate solution for running iOS tests in parallel locally and across many Macs.

Emcee allows you to run UI tests on many physical machines, distributing the work and getting the results of the test run faster. Shared queue manages the order of test execution. Emcee workers execute tests and maintain lifecycle of their simulators automatically. Emcee can generate the Junit and trace reports to make you see how the test run behaved on different machines.


  • Rich test plans using simple JSON file format

  • Automatic simulator lifecycle management

  • Per-test timeouts, simulator settings, environment variables

  • Single test queue to run tests from multiple parallel pull requests

  • Prioritized jobs and job groups for different kinds of test runs

  • Load balancing of worker machines to achieve optimal parallelization performance

  • On-the-go maintenance of the workers

  • Integration into existing test management systems via plugins

  • Easy to use command line interface

  • Rich test discovery mechanism

  • Swift Package for using and extending Emcee the way you want

Getting started

In this guide will demonstrate how to use Emcee. We will use two MacOS machines to run unit and UI tests from a sample project. You can also use a single machine to try out Emcee to see if it works for your project. In this case, a single machine will act as a queue and a worker simultaneously. Alternatively, you can scale this guide to as many machines as you have.

If you encounter any issues while proceeding through the guide, please open an issue or reach out via https://t.me/emcee_ios.

Table of contents

  1. Setting up machines
  2. Building the sample project
  3. Running tests using Emcee
    1. Tests without a host application
    2. Tests with a host application
    3. XCUI tests
  4. Advanced Emcee configuration

Setting up machines

You will need to grant SSH access to your machines.

Expand to see how to set up your machines.

We will be using two machines: ios-build-machine77 and ios-build-machine78.


  • ios-build-machine77 will be a worker and a queue - it will provide workers with tests to execute and execute some of those tests.
  • ios-build-machine78 will be a worker - it will only execute tests.

Both machines are set up with a standard non-administrator user emcee and a qwerty password.

Install Xcode and sudo xcode-select --switch /Applications/Xcode.app on all of your machines.

We will use Xcode 13.0 (13A233) and the iOS 15.0 simulator runtime bundled with this Xcode. If you want to use a specific version of simulator runtime, proceed to Xcode -> Preferences... -> Components -> Simulators and install the runtime on all the worker machines, where you want the tests to execute with the specific runtime version.

Emcee uses ssh to deploy itself to the machines specified as queue and workers. Enable SSH in your System Preferences -> Sharing -> Remote Login. To open this pane execute:

$ open "x-apple.systempreferences:com.apple.preferences.sharing?Services_RemoteLogin"

Remote Login SSH Settings

Now make sure that machines are accessible by ssh. For example:

ssh emcee@ios-build-machine77

If your machines are not accessible by DNS, use their IP addresses instead. You can check IP address in System Preferences -> Sharing. Please note IP addresses may change over time. To open this pane execute:

$ open "x-apple.systempreferences:com.apple.preferences.sharing"

Building the sample project

In this step, we will build a sample project that features different types of tests. Xcode and xcodebuild will produce build artifacts in derived data.

Expand to see how to build the sample project for testing purposes.

You can run this step from either machine. Clone the sample project:

cd ~
git clone https://github.com/avito-tech/Emcee.git
cd Emcee/Samples/EmceeSample

To build the project, create a simulator:

xcrun simctl create '15.0' 'iPhone X' 'iOS15.0'

Now run xcodebuild:

xcodebuild build-for-testing \
	-project EmceeSample.xcodeproj \
	-destination "platform=iOS Simulator,name=15.0,OS=15.0" \
	-scheme AllTests \
	-derivedDataPath derivedData

Xcodebuild will place the build products in:


Running tests using Emcee

Now that the machines are ready, and the project is built, download Emcee on the same machine where you built the project by running:

curl -L https://github.com/avito-tech/Emcee/releases/download/16.0.0/Emcee -o Emcee && chmod +x Emcee

If you download Emcee using a browser you will need to clear attributes and set the executable bit:

xattr -c Emcee && chmod +x Emcee

With Emcee installed it is finally time to run the tests. The sample project includes 3 test types:

  • Tests that don't require a host application
  • Tests that require a host application
  • XCUI tests

Tests without a host application

Let's first run tests that don't require a host application. We will be using the runTests command:

./Emcee runTests \
	--queue ssh://emcee:qwerty@ios-build-machine77 \
	--worker ssh://emcee:qwerty@ios-build-machine77 \
	--worker ssh://emcee:qwerty@ios-build-machine78 \
	--device "iPhone X" \
	--runtime "15.0" \
	--test-bundle derivedData/Build/Products/Debug-iphonesimulator/EmceeSampleTestsWithoutHost.xctest \
	--junit tests_without_host_junit.xml

Here is what these options stand for:

  • --queue - is a URL of a machine that will serve workers with tests
  • --worker - is a URL of a machine that will execute tests that it queries from the queue
  • --device and --runtime - are options that specify which simulators will run the tests
  • --test-bundle - is a path to the xctest bundle
  • --junit - is a path to the JUnit xml that will contain the result of the test run

You can find more about all options accepted by runTests and how to specify them using Emcee runTests -h.

After the test finishes, Emcee will create a tests_without_host_junit.xml file. The JUnit report contains four testcase entries matching the four test methods from the EmceeSampleTestsWithoutHost.xctest test bundle.

<?xml version="1.0" encoding="UTF-8"?>
<testsuites name="xctest" tests="4" failures="1">
    <testsuite name="EmceeSampleTestsWithoutHost" tests="4" failures="1">
        <testcase classname="EmceeSampleTestsWithoutHost" name="test_0___from_tests_without_host___that_always_succeeds" timestamp="2021-12-29T01:15:16+03:00" time="0.012196063995361328"></testcase>
        <testcase classname="EmceeSampleTestsWithoutHost" name="test_1___from_tests_without_host___that_always_succeeds" timestamp="2021-12-29T01:15:27+03:00" time="0.02156198024749756"></testcase>
        <testcase classname="EmceeSampleTestsWithoutHost" name="test_2___from_tests_without_host___that_always_succeeds" timestamp="2021-12-29T01:15:36+03:00" time="0.021990060806274414"></testcase>
        <testcase classname="EmceeSampleTestsWithoutHost" name="test___from_tests_without_host___that_always_fails" timestamp="2021-12-29T01:15:31+03:00" time="0.1255110502243042">
            <failure message="failed - Failure from tests without host">/Users/emcee/Emcee/SampleProject/EmceeSampleTestsWithoutHost/EmceeSampleTestsWithoutHost.swift:17</failure>
            <failure message="failed - Failure from tests without host">/Users/emcee/Emcee/SampleProject/EmceeSampleTestsWithoutHost/EmceeSampleTestsWithoutHost.swift:17</failure>

For a more sophisticated test reporting mechanism such as Allure, check out the Plugins documentation.

Tests with a host application

Now let's try running tests that require a host application. Host application path is specified using the --app option. For example:

./Emcee runTests \
    --queue ssh://emcee:qwerty@ios-build-machine77 \
    --worker ssh://emcee:qwerty@ios-build-machine77 \
    --worker ssh://emcee:qwerty@ios-build-machine78 \
    --device "iPhone X" \
    --runtime "15.0" \
    --app derivedData/Build/Products/Debug-iphonesimulator/EmceeSample.app \
    --test-bundle derivedData/Build/Products/Debug-iphonesimulator/EmceeSample.app/PlugIns/EmceeSampleHostedTests.xctest \
    --junit tests_with_host_junit.xml

To get a visual confirmation that Emcee is running the tests, you can open the Simulator app on the worker machines:

open "$(xcode-select -p)"/Applications/Simulator.app

XCUI tests

Finally, we will run XCUI tests by adding a --runner option and changing the --test-bundle option to the XCUI test bundle:

./Emcee runTests \
    --queue ssh://emcee:qwerty@ios-build-machine77 \
    --worker ssh://emcee:qwerty@ios-build-machine77 \
    --worker ssh://emcee:qwerty@ios-build-machine78 \
    --device "iPhone X" \
    --runtime "15.0" \
    --runner derivedData/Build/Products/Debug-iphonesimulator/EmceeSampleUITests-Runner.app \
    --app derivedData/Build/Products/Debug-iphonesimulator/EmceeSample.app \
    --test-bundle derivedData/Build/Products/Debug-iphonesimulator/EmceeSampleUITests-Runner.app/PlugIns/EmceeSampleUITests.xctest \
    --junit ui_tests_junit.xml

This is how the test run will look:


Advanced Emcee configuration

Complete documentation is available in our Wiki.

runTests command allows you to get Emcee up and running quickly; however, it doesn't allow for a lot of configuration. On the other hand, runTestsOnRemoteQueue command allows for fine-grained control of how your tests execute. To get started with runTestsOnRemoteQueue check out the Queue Server Configuration and Test Arg File wiki pages.


Getting Around the Code

Emcee uses Swift Package Manager for building, testing and exposing the Swift packages.

To start exploring code open Package.swift in Xcode 13 or execute make open to generate and open Xcode project.


We are happy to accept your pull requests. If something does not work for you, please let us know by submitting an issue. Read the docs and suggest improvements to them as well!

General commands that help you with a development workflow:

  • To open a package in Xcode: make open
  • To generate Package.swift: make package
  • To build the binary into .build/debug/Emcee: make build
  • To run unit tests: make test

Package.swift file is generated automatically. You must update it before submitting a pull request (run make package). CI checks will fail if you forget to do so.



brew install libssh2


Stars: 182
Last commit: 4 hours ago
jonrohan Something's broken? Yell at me @ptrpavlik. Praise and feedback (and money) is also welcome.

Release Notes

Easy Peasy
1 week ago

We've conducted a bunch of interviews with teams who use Emcee. We were provided with nice feedback which we used to improve our product. In this release, we focus on ease of use and an easy first try experience.

Getting Started Guide with Pictures and Sample Project πŸ₯©

It is available right at README.

Just Run These Tests 🀬

We introduce a new command - runTests. A very similar one to a famous runTestsOnRemoteQueue but it is dedicated to opening the world of simplicity and clear setup for most Emcee users. It has the following syntax and options:

$ Emcee runTests -h

  • --queue: describes where should a queue be started. This argument may be repeated multiple times, in which case Emcee will use hosts one by one until it manages to start the queue. You must provide at least one value here.
  • --worker: describes where worker should be started. This argument may be repeated multiple times. It is required to provide at least one value.
  • --device: Device to run test on, e.g. iPhone X. Required. Note: iPhone SE generations might be tricky to use!
  • --runtime: Runtime to run test on, e.g. 15.0. Required.
  • --test-bundle: Location of an .xctest bundle which tests will be executed. Required.
  • --app: Location of an .app bundle. Optional. Please refer to our guide to learn more about tests with host app.
  • --runner: Location of an XX-Runner.app. Optional.
  • --test: Test to execute, e.g. ClassName/testMethod. Optional. If not specified, Emcee will run all tests. You can specify multiple tests to execute, e.g. --test Class/test1 --test Class/test2
  • --retries: How many retries to attempt to run each test successfully. Optional. By default it will retry tests once if failure happens.
  • --test-timeout: Maximum test execution duration. Optional. Default test duration limit is 180 seconds.
  • --junit: Path where the Junit report file should be created. Optional.
  • --trace: Path where the Chrome trace file should be created. Optional.

Let's explain --queue and --worker arguments. These are URLs which describe how to connect to a machine. Currently only SSH is supported. Some examples:

  • --queue ssh://emcee:pass@queue.example.com/Users/emcee/emceequeue.noindex: it means to run Emcee queue on a queue.example.com host, by authenticating with emcee username and pass password. The working directory will be located at /Users/emcee/emceequeue.noindex.
  • --worker ssh://emcee@worker.example.com/Users/emcee/emceeworker.noindex?custom_rsa: it means the queue will start its worker on worker.example.com. Worker will use /Users/emcee/emceeworker.noindex as its working directory. Also, Emcee will use emcee as username and ~/.ssh/custom_rsa key to auth against a worker host. This key is expected to be present on queue host.
  • --worker ssh://emcee@worker.example.com/Users/emcee/emceeworker.noindex#/absolute/path/to/custom_rsa: same as above, but queue will use a key from /absolute/path/to/custom_rsa.

Free HTTP Server for Everyone! 🌏

Emcee now contains a built-in HTTP server that will cover most of your needs. This significantly simplifies the flow and lowers the entry threshold.

You can pass local paths into runTests command. Provided local .app and .xctest bundles will be hosted via a built-in HTTP server transparently, allowing all workers to download artifacts in order to run tests.

You can also provide local paths inside test arg file which you pass into runTestsOnRemoteQueue, those will also be hosted via the built-in server. Handy!

And finally, you can provide a local queue server configuration file into runTestsOnRemoteQueue. Now there is no need to upload it to a HTTP server.

Other Goodies 🦚

Help me Dr. -h 🍑

You can now get help for any command by typing -h next to it, e.g. Emcee -h or Emcee runTests -h. Sounds like Emcee is ready for such kind of hi-tech.

Better errors πŸ’’

Should you provide an incorrect test arg file or queue configuration JSON file, Emcee will now print human-readable errors. You will be amazed. Here is one error for your consideration:

Failed to decode value for key "entries" in "test arg file": key "xcTestBundle" not found at entries[0].buildArtifacts

That is a crystal clear explanation of what went wrong, is it not?

Optional jobId β˜ƒοΈ

It wasn't clear for some of our users that jobId field in a test arg file should be unique. Now you can omit it, Emcee will generate a random jobId for you.

Test Retry Mode πŸ‘―β€β™€οΈ

You can now specify how you'd like your tests to be retried if they fail. In your test arg file's entries there is a new field testRetryMode. Possible values:

  • retryThroughQueue β€” if a test fails on a worker, it will be returned back to the queue. A queue will then retry this test on other workers, up to the specified number of retries. This is the default behavior. This allows the test to be executed on different hosts, potentially eliminating the problem of a broken environment (because every macOS installation in Universe is unique).

  • retryOnWorker β€” if the test fails, the same worker will perform retry.

Simulator Patching is Better πŸ“²

There was a bug (OMG) that resulted in redundant simulator patching (read: apply simulator settings). Now Emcee won't patch simulators if everything is patched.

Cacheless Workers are Now Possible πŸ’³

There is a way to disable worker cache. In queue server configuration, in worker specific settings, next to numberOfSimulators field there are two more fields:

  • maximumCacheSize β€” maximum cache size in bytes.
  • maximumCacheTTL β€” maximum TTL for any cached item, in seconds.

You can set 0 these fields, and it will disable cache entirely. This is handy if you want to debug something.

Prevent Emcee from Cleaning Runner Output πŸƒ

You can now stop workers from removing all test artifacts automatically after a test finishes and plugins terminate. In a test arg file's entries there is a new field runnerWasteCleanupPolicy. Possible values:

  • clean β€” default value, it means everything will be deleted
  • keep β€” all created files will be preserved.

Log Capturing Mode πŸ“

You can now control what logs should be captured during a test run. These logs are obtained from xcresult bundles after the tests finish. In the test arg file's entries there is a new field logCapturingMode. Possible values:

  • allLogs β€” all log messages will be captured
  • onlyCrashLogs β€” only logs that look like crash logs will be captures
  • noLogs β€” no logs will be captured

Where without dyld

You can now insert dynamic libraries into a test. In a test arg file's entries there is a new field userInsertedLibraries. This is an array of paths. These paths will be passed as DYLD_INSERT_LIBRARIES env into the test. Combine it with state of the art macOS imaging features, with a fact that tests are being executed via xcodebuild (so it can expand __TESTBUNDLE__ and other strings - look at man xcodebuild.xctestrun), and this will provide you some additional flexibility for your test execution process.

Try it Today! 🧨

  • Below is a universal binary (arm64 & x64) for your convenience! It even has built-in libssh, so you can use it with ease.
  • If you download Emcee binary from GitHub, do not forget to remove quarantine attribute: xattr -c Emcee
  • Please rebuild your plugins. v15 API is not compatible with v16.

Full Changelog: https://github.com/avito-tech/Emcee/compare/15.0.0...16.0.0

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