Set up Github Actions CI (#440)

* Adjust tests: update Pip URLs, update expected output to match newer code
* Test library: improve failure message to eliminate the illusion of extra leading space in "actual" output
* Use Bats 1.2.0 like Pyenv
* Install greadlink for old MacOS
* Delete duplicate test

.github/workflows/tests.yml

@@ -0,0 +1,37 @@
+name: tests
+on: [pull_request, push]
+jobs:
+  tests:
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-22.04
+          - ubuntu-20.04
+          - macos-12
+          - macos-11
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      # Normally, we would use the superbly maintained...
+      # - uses: actions/setup-python@v2
+      #   with:
+      #    python-version: ${{ matrix.python-version }}
+      # ... but in the repo, we want to test pyenv builds on Ubuntu
+      # - run: |
+          # sudo apt-get install -y build-essential libssl-dev zlib1g-dev libbz2-dev \
+              # libreadline-dev libsqlite3-dev wget curl llvm libncurses5-dev libncursesw5-dev \
+              # xz-utils tk-dev libffi-dev liblzma-dev python-openssl git
+      # https://github.com/pyenv/pyenv#installation
+      #- env:
+      #    PYENV_ROOT: /home/runner/work/pyenv/pyenv
+      #  run: |
+      #    echo $PYENV_ROOT
+      #    echo "$PYENV_ROOT/shims:$PYENV_ROOT/bin" >> $GITHUB_PATH
+      # macos-11 Github Actions env has an old `readlink` and lacks `greadlink` which causes Bats to break
+      - run: |
+          if [[ $RUNNER_OS == "macOS" ]] && [[ $(sw_vers -productVersion | awk -F. '{print $1}') -lt 12 ]]; then
+            brew install coreutils
+          fi
+      - run: git clone https://github.com/bats-core/bats-core.git --depth=1 -b v1.2.0 bats
+      - run: bats/bin/bats --tap test