Add integration test (#217)

Fixes #215.

The workflow is adapted from the setup in SciML and ChainRules. Test times could be reduced with a setup of the Turing tests similar to Bijectors (which was inspired by SciML) that allows to run a subset of tests based on an environment variable: https://github.com/TuringLang/Bijectors.jl/blob/ad6b01c4a214562ef845ab3b5a0a296b348e1ba9/test/runtests.jl#L29

Author: devmotion

.github/workflows/IntegrationTest.yml

@@ -0,0 +1,51 @@
+name: IntegrationTest
+
+on:
+  push:
+    branches:
+      # This is where pull requests from "bors r+" are built.
+      - staging
+      # This is where pull requests from "bors try" are built.
+      - trying
+      # Build the master branch.
+      - master
+
+jobs:
+  test:
+    name: ${{ matrix.package.repo }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        package:
+          - {user: TuringLang, repo: Turing.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

@@ -1,7 +1,8 @@
 # DynamicPPL.jl
 
-[![Build Status](https://github.com/TuringLang/DynamicPPL.jl/workflows/CI/badge.svg?branch=master)](https://github.com/TuringLang/DynamicPPL.jl/actions?query=workflow%3ACI+branch%3Amaster)
-[![Build Status](https://github.com/TuringLang/DynamicPPL.jl/workflows/JuliaNightly/badge.svg?branch=master)](https://github.com/TuringLang/DynamicPPL.jl/actions?query=workflow%3AJuliaNightly+branch%3Amaster)
+[![CI](https://github.com/TuringLang/DynamicPPL.jl/workflows/CI/badge.svg?branch=master)](https://github.com/TuringLang/DynamicPPL.jl/actions?query=workflow%3ACI+branch%3Amaster)
+[![JuliaNightly](https://github.com/TuringLang/DynamicPPL.jl/workflows/JuliaNightly/badge.svg?branch=master)](https://github.com/TuringLang/DynamicPPL.jl/actions?query=workflow%3AJuliaNightly+branch%3Amaster)
+[![IntegrationTest](https://github.com/TuringLang/DynamicPPL.jl/workflows/IntegrationTest/badge.svg?branch=master)](https://github.com/TuringLang/DynamicPPL.jl/actions?query=workflow%3AIntegrationTest+branch%3Amaster)
 [![Coverage Status](https://coveralls.io/repos/github/TuringLang/DynamicPPL.jl/badge.svg?branch=master)](https://coveralls.io/github/TuringLang/DynamicPPL.jl?branch=master)
 [![Codecov](https://codecov.io/gh/TuringLang/DynamicPPL.jl/branch/master/graph/badge.svg)](https://codecov.io/gh/TuringLang/DynamicPPL.jl)
 [![ColPrac: Contributor's Guide on Collaborative Practices for Community Packages](https://img.shields.io/badge/ColPrac-Contributor's%20Guide-blueviolet)](https://colprac.sciml.ai/)

bors.toml

@@ -14,7 +14,8 @@ status = [
   "test (1.%, windows-latest, x64, 1)",
   "test (1.%, windows-latest, x64, 2)",
   "test (1, windows-latest, x64, 1)",
-  "test (1, windows-latest, x64, 2)"
+  "test (1, windows-latest, x64, 2)",
+  "Turing.jl"
 ]
 delete_merged_branches = true
 # Require at least on approval of a project member.