diff --git a/calculator/test.js b/calculator/test.js
index e8e7212..e07027f 100644
--- a/calculator/test.js
+++ b/calculator/test.js
@@ -57,10 +57,12 @@ global.load = () => {};
 
 
 // --- Load calculator app ---
+// We wrap the app code in a function that returns the buttonPress function,
+// so we can capture it and use it in our tests.
 const calculatorCode = fs.readFileSync(path.join(__dirname, 'calculator.app.js'), 'utf8');
-(function(require) {
-  eval(calculatorCode);
-})((name) => {
+const wrappedCode = `(function(require) { ${calculatorCode}; return buttonPress; })`;
+const getButtonPress = eval(wrappedCode);
+const buttonPress = getButtonPress((name) => {
   if (name === "FontDylex7x13") {
     return { add: () => {} };
   }