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Contributing to Prebid.js

Contributions are always welcome. To contribute, fork Prebid.js, commit your changes, and open a pull request against the master branch.

Pull requests must have 80% code coverage before beign considered for merge. Additional details about the process can be found here.

Issues contains documentation that may help answer questions you have about using Prebid.js. If you can't find the answer there, try searching for a similar issue on the issues page. If you don't find an answer there, open a new issue.


If you have a documentation issue or pull request, please open a ticket or PR in the documentation repository.

Writing Tests

Prebid uses Mocha and Chai for unit tests. Sinon provides mocks, stubs, and spies. Karma runs the tests and generates code coverage reports at build/coverage/lcov/lcov-report/index.html.

Tests are stored in the test/spec directory. Tests for Adapters are located in test/spec/adapters. They can be run with the following commands:

  • gulp test - run the test suite once (npm test is aliased to call gulp test)
  • gulp serve - run the test suite once, but re-run it whenever a file in the src or test directory is modified

Before a Pull Request will be considered for merge:

  • All new and existing tests must pass
  • Added or modified code must have greater than 80% coverage

If you are submitting an adapter, you can also use the Hello World example page to test integration with your server.

Test Guidelines

When you are adding code to Prebid.js, or modifying code that isn't covered by an existing test, test the code according to these guidelines:

  • If the module you are working on is already partially tested by a file within the test/spec directory, add tests to that file
  • If the module does not have any tests, create a new test file
  • Group tests in a describe block
  • Test individual units of code within an it block
  • Within an it block, it may be helpful to use the "Arrange-Act-Assert" pattern
    • Arrange: set up necessary preconditions and inputs
      • e.g., creating objects, spies, etc.
    • Act: call or act on the unit under test
      • e.g., call the function you are testing with the parameters you set up
    • Assert: check that the expected results have occurred
      • e.g., use Chai assertions to check that the expected output is equal to the actual output
  • Test the public interface, not the internal implementation
  • If you need to check adloader.loadScript in a test, use a stub rather than a spy. spys trigger a network call which can result in a script error and cause unrelated unit tests to fail. stubs will let you gather information about the adloader.loadScript call without affecting external resources
  • When writing tests you may use ES2015 syntax if desired

Test Examples

Prebid.js already has many tests. Read them to see how Prebid.js is tested, and for inspiration:

  • Look in test/spec and its subdirectories
  • Tests for bidder adaptors are located in test/spec/modules

A test module might have the following general structure:

// import or require modules necessary for the test, e.g.:
import { expect } from 'chai';  // may prefer 'assert' in place of 'expect'
import adapter from 'src/adapters/<adapter>';

describe('<Adapter>', () => {
  it('<description of unit or feature being tested>', () => {
    // Arrange - set up preconditions and inputs
    // Act - call or act on the code under test
    // Assert - use chai to check that expected results have occurred

  // Add other `describe` or `it` blocks as necessary