enable CI

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  run:
+    name: "Build using Racket '${{ matrix.racket-version }}' (${{ matrix.racket-variant }})"
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        racket-version: ["6.6", "6.7", "6.8", "6.9", "6.10.1", "6.11", "6.12", "7.0", "7.1", "7.2", "7.3", "7.4", "7.5", "7.6", "7.7", "7.8", "7.9", "current"]
+        racket-variant: ["BC", "CS"]
+        # CS builds are only provided for versions 7.4 and up so avoid
+        # running the job for prior versions.
+        exclude:
+          - {racket-version: "6.6",    racket-variant: "CS"}
+          - {racket-version: "6.7",    racket-variant: "CS"}
+          - {racket-version: "6.8",    racket-variant: "CS"}
+          - {racket-version: "6.9",    racket-variant: "CS"}
+          - {racket-version: "6.10.1", racket-variant: "CS"}
+          - {racket-version: "6.11",   racket-variant: "CS"}
+          - {racket-version: "6.12",   racket-variant: "CS"}
+          - {racket-version: "7.0",    racket-variant: "CS"}
+          - {racket-version: "7.1",    racket-variant: "CS"}
+          - {racket-version: "7.2",    racket-variant: "CS"}
+          - {racket-version: "7.3",    racket-variant: "CS"}
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@master
+
+    - uses: Bogdanp/setup-racket@v0.11
+      with:
+        distribution: 'full'
+        version: ${{ matrix.racket-version }}
+        variant: ${{ matrix.racket-variant }}
+
+    - name: install describe and its dependencies
+      run: raco pkg install --auto --batch
+
+    - name: run the tests
+      run: xvfb-run raco test -j 4 -p txexpr