Writing Package Tests
=====================

The tests under the `PackageTests` directory define and build packages which
exercise various components of Cabal. Each test case is an `HUnit` test. The
entry point for the test suite, where all the test cases are listed, is
`PackageTests.hs`. There are utilities for calling the stages of Cabal's build
process in `PackageTests/PackageTester.hs`; have a look at an existing test case
to see how they're used.

It is very important that package tests use the in-place version of Cabal,
rather than the system version. Several long-standing bugs in the test suite
were caused by testing the system (rather than the newly-compiled) version of
Cabal. There are two places where the system Cabal can accidentally be invoked:
1. Compiling `Setup.hs`. `runghc` needs to be told about the in-place package
database. This issue should be solved for all future package tests; see
`compileSetup` in `PackageTests/PackageTester.hs`.
2. Compiling a package which depends on Cabal. In particular, packages with
`detailed` type test suites depend on the Cabal library directly, so it is
important that they are configured to use the in-place package database. The
test suite already creates a stub `PackageSpec` for this case; see
`PackageTests/BuildTestSuiteDetailedV09/Check.hs` to see how it is used.