Add integration test

Author: devmotion

.github/workflows/IntegrationTest.yml

@@ -0,0 +1,46 @@
+name: IntegrationTest
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  test:
+    name: ${{ matrix.package.repo }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        package:
+          - {user: TuringLang, repo: DynamicPPL.jl}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: julia-actions/setup-julia@v1
+        with:
+          version: 1
+          arch: x64
+      - uses: julia-actions/julia-buildpkg@latest
+      - name: Clone Downstream
+        uses: actions/checkout@v2
+        with:
+          repository: ${{ matrix.package.user }}/${{ matrix.package.repo }}
+          path: downstream
+      - name: Load this and run the downstream tests
+        shell: julia --color=yes --project=downstream {0}
+        run: |
+          using Pkg
+          try
+            # force it to use this PR's version of the package
+            Pkg.develop(PackageSpec(path="."))  # resolver may fail with main deps
+            Pkg.update()
+            Pkg.test()  # resolver may fail with test time deps
+          catch err
+            err isa Pkg.Resolve.ResolverError || rethrow()
+            # If we can't resolve that means this is incompatible by SemVer and this is fine
+            # It means we marked this as a breaking change, so we don't need to worry about
+            # Mistakenly introducing a breaking change, as we have intentionally made one
+            @info "Not compatible with this release. No problem." exception=err
+            exit(0)  # Exit immediately, as a success
+          end

README.md

@@ -1,6 +1,7 @@
 # AbstractPPL.jl
 
 [![CI](https://github.com/TuringLang/AbstractPPL.jl/workflows/CI/badge.svg?branch=master)](https://github.com/TuringLang/AbstractPPL.jl/actions?query=workflow%3ACI+branch%3Amaster)
+[![IntegrationTest](https://github.com/TuringLang/AbstractPPL.jl/workflows/IntegrationTest/badge.svg?branch=master)](https://github.com/TuringLang/AbstractPPL.jl/actions?query=workflow%3AIntegrationTest+branch%3Amaster)
 [![Coverage Status](https://coveralls.io/repos/github/TuringLang/AbstractPPL.jl/badge.svg?branch=master)](https://coveralls.io/github/TuringLang/AbstractPPL.jl?branch=master)
 [![Codecov](https://codecov.io/gh/TuringLang/AbstractPPL.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/TuringLang/AbstractPPL.jl)