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This guide assumes that you:
Piwik Core contains a suite of tests used to make sure that Piwik works properly and that new commits do not introduce new bugs. These are the types of tests in this suite: unit tests, integration tests, system tests and ui tests.
Unit tests test individual classes isolated from the rest of the code to make sure they work correctly as a unit.
Integration tests test several parts working together, e.g. a test using a database.