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Testing

Testing Reaction breaks down into two broad categories:

• Manual or automated acceptance testing
• Automated code tests

The automated code tests category can be further divided into two main types:

• Jest unit tests
• Jest integration tests

The aim is to have full test coverage with Jest tests.

Unit vs. Integration

Unit tests simulate all possible outputs of a single function or component, given various inputs. They mock all external function calls in order to achieve a pure test of only that one function's logic.

Integration tests check to make sure that various functions or components are working together properly.

For example, if you write a GraphQL shop resolver and a tags resolver, each of those must have a unit test that determines whether the shop or tags list, respectively, is correctly returned. But assuming that a shop has a tags field, your shop unit test will be mocking or otherwise ignoring the output of the tags resolver. To ensure that the two resolvers work together to produce the correct shop.tags field, you need an integration test.

The different between a unit test and an integration test is not always clear cut. You might choose to test two functions together but still mock all other functions that they call. This is technically an integration test, but might be best written in a unit testing pattern.

For this reason, think of the terms "unit" and "integration" more as ends of a spectrum, where the "unit" end mocks everything and tests in complete isolation while the "integration" end mocks nothing and is essentially like running the app itself.

In practice, in the Reaction codebase, the primary distinction is that integration tests are all written in the /tests folder and can make use of a fake, in-memory version of MongoDB, while unit tests have no mock database and are written in files throughout the code, with names similar to the name of the file they test.

When To Run Tests

• If you are changing code and submitting a pull request, you should run all tests on your machine prior to submitting the pull request for review. Use the reaction test or npm test command to do this.
• For all pull requests, CircleCI automatically runs all unit and integration tests and will not allow merging until they all pass.

Further Reading

For a walkthrough on how to write test for reaction's plugin:

• How to write tests for plugins

For Jest, see the following:

• Running Jest Unit Tests
• Running Jest Integration Tests
• Writing Jest Unit tests
• Writing Jest Integration Tests
• Writing Jest Tests for React Components
• Creating Test Data
• Jest Tips
• The official Jest documentation

For acceptance testing, see the Acceptance Testing section.