diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 282b637..ba27c47 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -15,11 +15,22 @@ jobs:
         uses: actions/checkout@v3
 
       - name: Run
+        id: run_test
         uses: ./
         with:
-          base-image: docker://rust:slim-buster
+          base-image: docker://ghcr.io/clementtsang/cargo-deb-arm
           derived-image: docker://rust:slim-buster
 
+      - name: Check
+        run: |
+          echo Result: ${{ steps.run_test.outputs.differs }}
+          if [ ${{ steps.run_test.outputs.differs }} == 'true' ]; then
+            exit 0
+          else
+            echo "differs should always be true!"
+            exit 1
+          fi
+
   test-always-false:
     runs-on: ubuntu-latest
     steps:
@@ -27,7 +38,18 @@ jobs:
         uses: actions/checkout@v3
 
       - name: Run
+        id: run_test
         uses: ./
         with:
-          base-image: docker://ghcr.io/clementtsang/cargo-deb-arm
+          base-image: docker://rust:slim-buster
           derived-image: docker://rust:slim-buster
+
+      - name: Check
+        run: |
+          echo Result: ${{ steps.run_test.outputs.differs }}
+          if [ ${{ steps.run_test.outputs.differs }} == 'false' ]; then
+            exit 0
+          else
+            echo "differs should always be false!"
+            exit 1
+          fi
diff --git a/README.md b/README.md
index 695d7a7..db29017 100644
--- a/README.md
+++ b/README.md
@@ -18,9 +18,26 @@ A required argument, this represents the "base" image you want to check against.
 As this is based on `skopeo`, it expects a string representing a container, and following a certain format
 (e.g. `docker://rust:slim-buster`). For more information, see [the `skopeo` README](https://github.com/containers/skopeo#skopeo-).
 
-### Outputs
+#### `derived-image`
 
 A required argument, this represents the "derived" image you want to check.
 
 As this is based on `skopeo`, it expects a string representing a container, and following a certain format
 (e.g. `docker://rust:slim-buster`). For more information, see [the `skopeo` README](https://github.com/containers/skopeo#skopeo-).
+
+### Outputs
+
+#### `differs`
+
+The action returns either `true` or `false`, indicating if the derived image differs from the base image (e.g. if derived does not contain the base, it returns `true`).
+
+## Example
+
+```yaml
+- name: Run
+id: run
+uses: ClementTsang/docker-check-base-image-diff@v0.0.1-alpha
+with:
+    base-image: docker://rust:slim-buster
+    derived-image: docker://ghcr.io/clementtsang/cargo-deb-arm
+```
diff --git a/action.yml b/action.yml
index daddafe..e610289 100644
--- a/action.yml
+++ b/action.yml
@@ -11,13 +11,14 @@ inputs:
     required: true
 outputs:
   differs:
-    description: "True or false"
-    value: ${{ steps.check.outputs.result }}
+    description: "Returns either true or false"
+    value: ${{ steps.check.outputs.differs }}
+
 runs:
   using: "composite"
   steps:
     - id: check
       shell: bash
       run: |
-        result=$(${{ github.action_path }}/check.sh ${{ inputs.base-image }} ${{ inputs.derived-image }})
-        echo "::set-output name=result::${result}"
+        RESULT=$(${{ github.action_path }}/check.sh ${{ inputs.base-image }} ${{ inputs.derived-image }})
+        echo "::set-output name=differs::$RESULT"
diff --git a/check.sh b/check.sh
index a54d6cb..1da51e4 100755
--- a/check.sh
+++ b/check.sh
@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -e
+
 BASE_LAYERS="$(skopeo inspect $1 | jq '.Layers')"
 DERIVED_LAYERS="$(skopeo inspect $2 | jq '.Layers')"