How to make AppVeyor use different versions of Emacs?

I want to use different versions of Emacs. I think I have to do this with the build matrix feature. I have searched around and cannot find how it is done.

I am going to use Choco to install my packages. The default version is Emacs24. But Emacs25 is available via an unofficial package.

I want to install different versions of the same software and run simultaneous builds.

Here is a wishful attempt of what it would look like (this doesn't work by the way):

matrix:
  - emacs: "24"
  - emacs: "25"

install:
  - ps : switch($emacs){ "24" {choco install emacs} "25" {choco install emacs64} default {echo "Emacs install fail"}}
  - refreshenv

build_script:
  - some script

Thanks in advance.

Solution

emacs is environment variable (not local one). Also YAML syntax require environment tag before matrix. You can always create configuration in UI and press Export YAML button if you are not sure. And finally not space between ps and :. Other than that config is good. Here is fixed one:

environment:
  matrix:
  - emacs: 24
  - emacs: 25

install:
  - ps: switch($env:emacs){ 24 {choco install emacs} 25 {choco install emacs64} default {echo "Emacs install fail"}}
  - refreshenv

Side note: I would recommend throw "Emacs install fail" instead of echo.