Migrate completion tests to Cucumber.

Also retire Fish 2.x + macOS test;
installation of custom brew didn't work out anymore.

.travis.yml

@@ -16,13 +16,6 @@ matrix:
             - sourceline: "ppa:fish-shell/release-3"
           packages:
             - fish
-    - os: osx
-      env: FISH=2
-      addons:
-        homebrew:
-          packages:
-            - 'test/Homebrew-Formula-fish-2.7.1.rb'
-          update: true # TODO: build should be green without, but isn't
     - os: osx
       env: FISH=3
       addons:
@@ -33,18 +26,19 @@ matrix:
 
 before_install:
   - curl -s "https://get.sdkman.io" | bash
-  - bash test/prepare_tests.sh
+  - bundle install --gemfile=test/Gemfile --no-cache
+  - uname -a; fish --version; sdk version; ruby --version; cucumber --version
 
 install:
   - mkdir -p "${HOME}"/.config/fish/{completions,conf.d,functions}
   - cp completions/* "${HOME}"/.config/fish/completions/
   - cp conf.d/* "${HOME}"/.config/fish/conf.d/
   - cp functions/* "${HOME}"/.config/fish/functions/
-  - uname -a; fish --version
 
 script:
-  - ruby test/completion.rb
-  - fish test/wrapper.fish
+  - (cd test && cucumber)
+  # TODO: Migrate these to Cucumber:
+  - bash test/prepare_tests.sh && fish test/wrapper.fish
   - fish test/reinitialize.fish
   - fish -c "sdk install crash 1.3.0; and sdk uninstall crash 1.3.0" > /dev/null && fish test/check_for_path_zombies.fish
   - bash test/remove_sdkman.sh > /dev/null && fish -c "echo 'y' | sdk" > /dev/null && fish -c "sdk version"