diff --git a/packages/snaps-controllers/coverage.json b/packages/snaps-controllers/coverage.json
index 28873f6536..0ef4e9b911 100644
--- a/packages/snaps-controllers/coverage.json
+++ b/packages/snaps-controllers/coverage.json
@@ -1,6 +1,6 @@
 {
-  "branches": 92.89,
+  "branches": 92.91,
   "functions": 96.71,
-  "lines": 98,
+  "lines": 98.01,
   "statements": 97.71
 }
diff --git a/packages/snaps-controllers/src/test-utils/webview.ts b/packages/snaps-controllers/src/test-utils/webview.ts
index 4838f57c95..2e9d1a9fe1 100644
--- a/packages/snaps-controllers/src/test-utils/webview.ts
+++ b/packages/snaps-controllers/src/test-utils/webview.ts
@@ -1,4 +1,9 @@
-import { base64ToBytes, bytesToString } from '@metamask/utils';
+import {
+  base64ToBytes,
+  bytesToBase64,
+  bytesToString,
+  stringToBytes,
+} from '@metamask/utils';
 
 import { WebViewMessageStream } from '../services/webview/WebViewMessageStream';
 
@@ -52,6 +57,11 @@ export function createWebViewObjects() {
     name: 'a',
     target: 'b',
     getWebView: mockGetWebViewA,
+    // For one of the streams, we test that a custom btoa function is used.
+    btoa: (data: string) => {
+      const bytes = stringToBytes(data);
+      return bytesToBase64(bytes);
+    },
   });
 
   const streamB = new WebViewMessageStream({