diff --git a/package-lock.json b/package-lock.json
index fe13b575..7420c0a7 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2484,6 +2484,12 @@
             "integrity": "sha512-s73XxOZ4zpt1edZYZzvhqFa6uvQc1vwUa0K0BdtIZgQMAJj9IbebH+JkgKZc9h+B05PKHLOTl4ajG1BmNrVZlw==",
             "dev": true
         },
+        "p-defer": {
+            "version": "3.0.0",
+            "resolved": "https://registry.npmjs.org/p-defer/-/p-defer-3.0.0.tgz",
+            "integrity": "sha512-ugZxsxmtTln604yeYd29EGrNhazN2lywetzpKhfmQjW/VJmhpDmWbiX+h0zL8V91R0UXkhb3KtPmyq9PZw3aYw==",
+            "dev": true
+        },
         "p-is-promise": {
             "version": "3.0.0",
             "resolved": "https://registry.npmjs.org/p-is-promise/-/p-is-promise-3.0.0.tgz",
diff --git a/package.json b/package.json
index bb0a9505..afb71981 100644
--- a/package.json
+++ b/package.json
@@ -65,6 +65,7 @@
         "ava": "^3.3.0",
         "changelog-updater": "^1.1.0",
         "nyc": "^15.0.0",
+        "p-defer": "^3.0.0",
         "sort-on": "^4.1.0",
         "typescript": "^3.7.5"
     },
diff --git a/src/bundle-orchastrator.test.ts b/src/bundle-orchastrator.test.ts
index daa8fac0..317de758 100644
--- a/src/bundle-orchastrator.test.ts
+++ b/src/bundle-orchastrator.test.ts
@@ -1,5 +1,5 @@
 import test, { ExecutionContext } from "ava";
-import { BundleOrchastrator } from "./bundle-orchastrator.js";
+import { BundleOrchastrator, ResultsCallback } from "./bundle-orchastrator.js";
 import intoStream from "into-stream";
 import getStream from "get-stream";
 import { Readable, Stream } from "stream";
@@ -7,6 +7,7 @@ import Vinyl from "vinyl";
 import { resolve as resolvePath } from "path";
 import sortOn from "sort-on";
 import { mapAvaLoggerToStandard } from "./test-util.js";
+import pDefer from "p-defer";
 
 /**
  * Returns a pretend bundle for testing purposes.
@@ -70,6 +71,11 @@ interface IBundleBuilderFlags {
      * Don't include any script bundles.
      */
     noScriptBundles?: boolean;
+
+    /**
+     * Results callback to include.
+     */
+    resultsCallback?: ResultsCallback;
 }
 
 /**
@@ -107,10 +113,23 @@ function buildBundler(t: ExecutionContext, flags: IBundleBuilderFlags = {}) {
             Scripts: bundleFactoryJs,
             Styles: bundleFactoryCss,
         },
+        flags.resultsCallback
+            ? flags.resultsCallback
+            : undefined,
     );
 }
 
 test("Bundles with all dependencies met", async t => {
+    t.plan(3);
+
+    const resultsCallbackCompletion = pDefer();
+    const resultsCallback: ResultsCallback = function (results) {
+        // Results data is based on a clone of the actual Vinyl files, length is enough for now
+        t.is(results.scripts.size, 1);
+        t.is(results.styles.size, 1);
+        resultsCallbackCompletion.resolve();
+    };
+
     const result = await getStream.array(
         intoStream.object([
             new Vinyl({ path: resolvePath("./123/bar.js") }),
@@ -118,7 +137,7 @@ test("Bundles with all dependencies met", async t => {
             new Vinyl({ path: resolvePath("./abc/foo.css") }),
             new Vinyl({ path: resolvePath("./abc/foo.js") }),
         ])
-            .pipe(buildBundler(t))
+            .pipe(buildBundler(t, { resultsCallback }))
     ) as Vinyl[];
 
     t.deepEqual(
@@ -137,6 +156,8 @@ test("Bundles with all dependencies met", async t => {
             'history'
         )
     );
+
+    await resultsCallbackCompletion.promise;
 });
 
 /**