ContractHarness class final

The contract test harness: checks that the modules and roles of a registry follow the rules of the module model, the way the pipeline would generate them in every combination that matters.

For a module it builds an app for every provider of the role of its variants, every provider of each role it requires, each subset of the roles it only uses with every provider of each of them, and every provider of a role whose package it contributes. For a role it builds an app for each of its providers, with every provider of each role the provider requires, and each subset of the roles the role uses with every provider of each of them. It leaves out a combination of providers that would give an app two providers of a role that takes one, unless every combination would, so that the cases report why. uncheckedProviders lists each provider of a role of a module that none of the apps of the module has. Each app goes through the stages 3 to 5 of the pipeline, in a run without a terminal that skips external setup, as the Flutter job generates apps; stage 5 includes checkTemplateTags, and the harness adds missingTemplateTags and reports templates with {{ that mason would copy as they are. Unless render is off, the harness then makes the roles' choices (stage 7) with the options of the case, renders the app in memory (stage 8) and checks the rendered code with checkRendered. A question of a role that the options leave open, such as the start screen of an app with several, gets the answer of a user who presses Enter: the default, or the first choice. The result has the options that make the same choice without asking (ContractResult.answers).

It depends on no test framework, so the tests of any package can use it.