added definition of integration testing (#122)

Author: dlavender4

quality-checks.md

@@ -35,7 +35,7 @@ We rate our applications against each of these checks as follows:
 | Quality check          | Classification  | Applicability | What it means                                                                                | Why we care                                                                                                                                                                                                                                                               | Tolerances for green                               | Endorsed tools / configuration                                                | Further details                                                                                               |
 | :--------------------- | :-------------- | :------------ | :------------------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | :------------------------------------------------- | :---------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------ |
 | Unit tests             | Functionality   | Universal     | Logic tests for individual blocks of code, e.g. individual methods                           | This is the quickest (to execute) type of functional test, so these are essential to achieve both rapid and thorough functional testing                                                                                                                                   | Builds fail if any tests fail                      | -                                                                             | [Test practices](./practices/testing.md)                                                                      |
-| Integration tests      | Functionality   | Universal     |                                                                                              |                                                                                                                                                                                                                                                                           | Builds fail if any tests fail                      |                                                                               |                                                                                                               |
+| Integration tests      | Functionality   | Universal     | Check interactions with other components and dependant systems. e.g. across microservices, authentication layers, database, third-party systems. Ideally includes full end-to-end testing across all components.    | When components are developed in isolation, it's vital that we regularly test them working together. Changes in one component can break the whole system.   | Builds fail if any tests fail                      |                                                                               |                                                                                                               |
 | API / contract tests   | Functionality   | Contextual    |                                                                                              |                                                                                                                                                                                                                                                                           | Builds fail if any tests fail                      |                                                                               |                                                                                                               |
 | UI tests               | Functionality   | Contextual    |                                                                                              |                                                                                                                                                                                                                                                                           | Builds fail if any tests fail                      |                                                                               |                                                                                                               |
 | Secret scanning        | Security        | Universal     | Check for secrets (e.g. passwords, IP addresses, etc) accidentally included in software code | This protects us against accidentally leaking secrets (in source code) which could compromise the security of the application                                                                                                                                             | Builds fail if any unexpected secrets are detected | TBC                                                                           | TBC                                                                                                           |