Clarify chain of testing between apps and APIs
Clarify chain of testing between apps and APIs

In response to: [^1].

[^1]: https://github.com/alphagov/govuk-developer-docs/pull/3498#discussion_r866593729

alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs,alphagov/govuk-developer-docs