Update JS HBS helper tests

packages/string-templates/test/javascript.spec.js

@@ -4,7 +4,21 @@ const processJS = (js, context) => {
   return processStringSync(encodeJSBinding(js), context)
 }
 
+describe("Test the JavaScript helper in Node", () => {
+  it("should not execute JS in Node", () => {
+    const output = processJS(`return 1`)
+    expect(output).toBe("JS bindings are not executed in a Node environment")
+  })
+})
+
 describe("Test the JavaScript helper", () => {
+  // JS bindings do not get evaluated on the server for safety.
+  // Since we want to run SJ for tests, we fake a window object to make
+  // it think that we're in the browser
+  beforeEach(() => {
+    window = {}
+  })
+
   it("should execute a simple expression", () => {
     const output = processJS(`return 1 + 2`)
     expect(output).toBe("3")