How to test with multiple versions of a dependency in CI

[nsajko]

I’d like to support more than one incompatible version of a dependency from a package extension.

How to test with all relevant versions of the dependency in CI?

[gdalle]

I had a similar problem with DifferentiationInterface.jl, where I need to test compatibility with a dozen different autodiff packages and pairs thereof. I solved it by creating several test “groups”, defined by an environment variable.
This environment variable is set in CI (possibly using entries from the workflow matrix), and then queried in runtests.jl. You can take a look at the following files: Test.yml, runtests.jl.

Also related:

• How to test package with different sets of test dependencies
• Different test dependencies for different Julia versions?