Fix idb test (#1996)

Summary:
Pull Request resolved: https://github.com/facebook/flipper/pull/1996

Erm, I'm a bit of a dummy. I didn't mock the access check, so it would actually
rely on idb being installed to run the tests correctly. Without, we'd fail like here
on GitHub: https://github.com/facebook/flipper/runs/2021551466

I couldn't quite figure out how to mock `fs.promises.access`, so I made the constructor
configurable, which doesn't seem that bad, actually.

Reviewed By: mweststrate

Differential Revision: D26778428

fbshipit-source-id: 120b8060ad3ccb1cecd8ce2b208733d5e1090a72

desktop/app/src/utils/IOSBridge.tsx

@@ -65,8 +65,11 @@ function xcrunStartLogListener(udid: string) {
   );
 }
 
-export async function makeIOSBridge(idbPath: string): Promise<IOSBridge> {
-  if (await isAvailable(idbPath)) {
+export async function makeIOSBridge(
+  idbPath: string,
+  isAvailableFn: (idbPath: string) => Promise<boolean> = isAvailable,
+): Promise<IOSBridge> {
+  if (await isAvailableFn(idbPath)) {
     return {
       startLogListener: idbStartLogListener.bind(null, idbPath),
     };

desktop/app/src/utils/__tests__/IOSBridge.node.tsx

@@ -38,7 +38,7 @@ test('uses xcrun with no idb', async () => {
 });
 
 test('uses idb when present', async () => {
-  const ib = await makeIOSBridge('/usr/local/bin/idb');
+  const ib = await makeIOSBridge('/usr/local/bin/idb', async (_) => true);
   ib.startLogListener('deadbeef');
 
   expect(spawn).toHaveBeenCalledWith(