Add working Linux tests

Author: adam-fowler

.github/workflows/build.yml

@@ -8,22 +8,37 @@ on:
     branches: [ master ]
     paths-ignore: [ README.md ]
 jobs:
-  build:
-    name: Build and test on ${{ matrix.os }}
-    runs-on: ${{ matrix.os }}
-    strategy:
-      matrix:
-        os: [macos-10.15, macos-latest, ubuntu-18.04, ubuntu-20.04]
+  macos:
+    name: Build and test on macos-latest
+    runs-on: macOS-latest
     steps:
     - uses: actions/checkout@v2
-    - name: Set code coverage path 
+    - name: Set code coverage path
       run: echo "codecov_path=$(swift test --show-codecov-path)" >> $GITHUB_ENV
     - name: Test and publish code coverage to Code Climate
       uses: paulofaria/codeclimate-action@master
-      if: matrix.os == 'macos-10.15'
       env:
         CC_TEST_REPORTER_ID: ${{secrets.CC_TEST_REPORTER_ID}}
       with:
         downloadUrl: https://github.com/paulofaria/test-reporter/releases/download/0.9.0/test-reporter-0.9.0-darwin-amd64
         coverageCommand: swift test --enable-test-discovery --enable-code-coverage
         coverageLocations: ${{ env.codecov_path }}:lcov-json
+
+  linux:
+    name: Build and test on ${{ matrix.tag }}-${{ matrix.os }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os:
+          - focal
+          - bionic
+        tag:
+          - swift:5.3
+          - swift:5.4
+    container:
+      image: ${{ matrix.tag }}-${{ matrix.os }}
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+    - name: Test
+      run: swift test --enable-test-discovery --enable-code-coverage --sanitize=thread