Add compatibility testing

.github/workflows/compatibility.yml

@@ -0,0 +1,43 @@
+name: Backwards Compatibility Tests
+
+on: ["workflow_dispatch", "pull_request"]
+
+jobs:
+  compatibility_test:
+    strategy:
+      matrix:
+        clojure_version: ['1.8.0', '1.9.0', '1.10.0', '1.11.0', '1.12.0']
+
+    concurrency:
+      group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}-${{ matrix.clojure_version }}
+      cancel-in-progress: true
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout Repository
+      uses: actions/checkout@v4.2.0
+
+    - name: Print concurrency group
+      run: echo '${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}'
+
+    - name: Cache maven dependencies
+      uses: actions/cache@v4
+      env:
+          cache-name: cache-maven
+      with:
+          path: ~/.m2
+          save-always: true
+          key: ${{ runner.os }}-clj-${{ hashFiles('**/project.clj') }}
+          restore-keys: |
+            ${{ runner.os }}-clj
+
+    - name: Install Clojure Dependencies
+      run: lein deps
+
+    - name: Override Clojure Version
+      run: lein change :dependencies:org.clojure/clojure set '"${{ matrix.clojure_version }}"'
+
+    - name: Run all tests
+      run: lein test
+

README.md

@@ -19,6 +19,11 @@ To use it, add the following as a dependency in your project.clj file:
 The next time you build your application, [Leiningen](https://leiningen.org/) or [deps.edn](https://clojure.org/guides/deps_and_cli) should pull it automatically.
 Alternatively, you may clone or fork the repository to work with it directly.
 
+### Clojure Version Compatibility
+
+clj-xml runs its test suite in a matrix, replacing the clojure version with multiple previous versions of the language.
+If your project is not running the most recent version of clojure, please consult the most recent compatibility testing results in the [CI/CD pipeline](https://github.com/Wall-Brew-Co/clj-xml/actions/workflows/compatibility.yml).
+
 ## Public Functions
 
 ### XML Parsing