diff --git a/Cargo.lock b/Cargo.lock
index 7102f94187..e25723ff17 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5797,6 +5797,7 @@ dependencies = [
  "spin-app",
  "spin-loader",
  "spin-manifest",
+ "spin-testing",
  "spin-trigger",
  "tempfile",
  "tokio",
diff --git a/crates/oci/Cargo.toml b/crates/oci/Cargo.toml
index 84eb53dccd..c60fb61331 100644
--- a/crates/oci/Cargo.toml
+++ b/crates/oci/Cargo.toml
@@ -27,3 +27,5 @@ tokio-util = "0.7.9"
 tracing = { workspace = true }
 walkdir = "2.3"
 
+[dev-dependencies]
+spin-testing = { path = "../testing" }
diff --git a/crates/oci/src/client.rs b/crates/oci/src/client.rs
index d98a3858bd..7bfb439b01 100644
--- a/crates/oci/src/client.rs
+++ b/crates/oci/src/client.rs
@@ -504,7 +504,6 @@ fn digest_from_url(manifest_url: &str) -> Option<String> {
 }
 
 // TODO: good use case for DeployableApp addition in cloud-plugin?  (Well, would want to move into spin to avoid circular deps)
-// TODO: add test
 async fn layer_count(locked: LockedApp) -> Result<usize> {
     let mut layer_count = 0;
     for c in locked.components {
@@ -539,4 +538,59 @@ mod test {
             digest
         );
     }
+
+    #[tokio::test]
+    async fn can_get_layer_count() {
+        use spin_app::locked::LockedComponent;
+
+        let working_dir = tempfile::tempdir().unwrap();
+        let source_dir = working_dir.path().join("foo");
+        let _ = tokio::fs::create_dir(source_dir.as_path()).await;
+        let file_path = source_dir.join("bar");
+        let _ = tokio::fs::File::create(file_path.as_path()).await;
+
+        let tests: Vec<(Vec<LockedComponent>, usize)> = [
+            (
+                spin_testing::from_json!([{
+                "id": "test-component",
+                "source": {
+                    "content_type": "application/wasm",
+                    "digest": "test-source",
+                },
+                }]),
+                1,
+            ),
+            (
+                spin_testing::from_json!([{
+                "id": "test-component",
+                "source": {
+                    "content_type": "application/wasm",
+                    "digest": "test-source",
+                },
+                "files": [
+                    {
+                        "source": format!("file://{}", file_path.to_str().unwrap()),
+                        "path": ""
+                    }
+                ]
+                }]),
+                2,
+            ),
+        ]
+        .to_vec();
+
+        for (components, expected) in tests {
+            let triggers = Default::default();
+            let metadata = Default::default();
+            let variables = Default::default();
+            let locked = LockedApp {
+                spin_lock_version: spin_app::locked::FixedVersion,
+                components,
+                triggers,
+                metadata,
+                variables,
+            };
+            assert_eq!(expected, layer_count(locked).await.unwrap());
+        }
+    }
 }
diff --git a/crates/testing/src/lib.rs b/crates/testing/src/lib.rs
index 5901ac8ab1..55e37a8e78 100644
--- a/crates/testing/src/lib.rs
+++ b/crates/testing/src/lib.rs
@@ -39,6 +39,7 @@ pub fn init_tracing() {
 }
 
 // Convenience wrapper for deserializing from literal JSON
+#[macro_export]
 macro_rules! from_json {
     ($($json:tt)+) => {
         serde_json::from_value(serde_json::json!($($json)+)).expect("valid json")