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testbot

testbot is a Continuous Integration (CI) tool designed for private GitHub monorepos.

To run a testbot instance, read Getting Started.

Why

Try testbot if you want to:

  1. start tests in < 3s after opening or editing a pull request
  2. run only the tests relevant to the change
  3. control your caches
  4. avoid leaking code, credentials, or data to a third-party CI provider

Common causes of slow-starting tests on hosted CI services are multi-tenant queues and containerization. In those environments, noisy neighbors backlog the queues and containers have cache misses.

If you organize your code into a monorepo, your pull requests often will not need to run most tests.

Avoid testbot if you want to:

  1. run tests on an open source (public) repo
  2. prefer convenience of a hosted service over managing your own CI environment

How it works

Imagine a monorepo that contains some files like this:

.
├── ...
├── dashboard
│   └── Testfile
├── sdk
│   ├── go
│   │   └── Testfile
│   ├── node
│   │   └── Testfile
│   └── ruby
│       └── Testfile
├── server
│   └── Testfile

We open a GitHub pull request to add a new feature to the SDKs:

sdk/go/account.go             | 10 +++++-----
sdk/go/account_test.go        | 10 +++++-----
sdk/node/src/account.ts       | 10 +++++-----
sdk/node/test/account.ts      | 10 +++++-----
sdk/ruby/lib/account.rb       | 10 +++++-----
sdk/ruby/spec/account_spec.rb | 10 +++++-----
6 files changed, 60 insertions(+), 60 deletions(-)

A testbot farmer process on a server responds to the GitHub webhook by:

  • identifying the directories containing files that have changed
  • walking up the file hierarchy to find Testfiles for changed directories
  • saving test jobs to its backing Postgres database

Each Testfile defines test jobs for its directory. Ours might be:

$ cat $ORG/sdk/go/Testfile
tests: cd $ORG/sdk && go test -cover ./...
$ cat $ORG/sdk/node/Testfile
tests: cd $ORG/sdk/node && npm install && npm test
$ cat $ORG/sdk/ruby/Testfile
tests: $ORG/sdk/ruby/test.sh

Each line contains a name and command separated by a colon. The name appears in GitHub checks. The command is run by a testbot worker, which is continuously long polling testbot farmer via HTTP over TLS, asking for test jobs.

We run more testbot worker instances to increase test parallelism.

In this example, the tests for the Go, Node, and Ruby SDKs will begin to run almost simultaneously as different testbot worker processes pick them up.

Tests for dashboard and server will not run in this pull request because no files in their directories were changed.

Credit

Keith Rarick designed and implemented testbot in November 2017. Since then, engineers at Chain, Interstellar, and Pogo have been maintaining it and running it on a succession of internal monorepos.