add a GitHub workflow config

.github/workflows/ci.yml

@@ -0,0 +1,86 @@
+name: Test Time
+
+on:
+  push:
+  workflow_dispatch:
+  pull_request:
+
+jobs:
+  test-and-compile:
+    runs-on: ubuntu-latest
+    timeout-minutes: 14
+
+    permissions:
+      contents: read
+      packages: read
+
+    name: Test on OTP ${{matrix.otp}} / Elixir ${{matrix.elixir}}
+
+    strategy:
+      matrix:
+        otp: ['26.1.2']
+        elixir: ['1.15.7']
+
+    env:
+      MIX_ENV: "test"
+
+    services:
+      db:
+        image: postgres:12
+        ports: ['5432:5432']
+        env:
+          POSTGRES_PASSWORD: postgres
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Cache deps
+        id: cache-deps
+        uses: actions/cache@v3
+        env:
+          cache-name: cache-elixir-deps
+        with:
+          path: deps
+          key: ${{ runner.os }}-mix-${{ env.cache-name }}-${{ hashFiles('**/mix.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-mix-${{ env.cache-name }}-
+
+      - name: Cache compiled build
+        id: cache-build
+        uses: actions/cache@v3
+        env:
+          cache-name: cache-compiled-build
+        with:
+          path: _build
+          key: ${{ runner.os }}-mix-${{ env.cache-name }}-${{ hashFiles('**/mix.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-mix-${{ env.cache-name }}-
+            ${{ runner.os }}-mix-
+
+      - name: Clean to rule out incremental build as a source of flakiness
+        if: github.run_attempt != '1'
+        run: |
+          mix deps.clean --all
+          mix clean
+        shell: sh
+
+      - name: Install dependencies
+        run: mix deps.get
+
+      - name: Compiles without warnings
+        run: mix compile --warnings-as-errors
+
+      - name: Check Formatting
+        run: mix format --check-formatted
+
+      - name: Check for unused dependencies
+        run: mix deps.unlock --unused
+
+      - name: Run tests
+        run: mix test