Stabilize US bank account Lite tests

[jaynewstrom-stripe]

Summary

• Make the Financial Connections Lite test driver support either server-controlled initial pane order.
• Poll all valid WebView test IDs together and return the selector that matched.
• Include the attempted selectors and final Espresso exception when WebView polling times out.

Motivation

TestUSBankAccount#testUSBankAccountLiteSuccess intermittently failed after 30 seconds while waiting for institution-default.

The Financial Connections frontend flag bank_connections_enable_select_institution_first controls whether institution-default or agree-button is rendered first. The Android test driver hard-coded institution-default followed by agree-button, so runs assigned the opposite flow variant waited for an element that was not expected to exist on that pane.

This fix works by polling both valid initial selectors during the same timeout. Once one appears, the driver records which selector matched, clicks it, and waits for the other pane. The cancellation flow similarly waits until either valid initial pane is ready before pressing Back. This follows the actual server-selected ordering instead of trying to hide the mismatch with a longer timeout.

Testing

• Added tests

• Modified tests

• Manually verified

• Temporarily wrapped TestRules with ShampooRule(20) and ran testUSBankAccountLiteSuccess on pixel2api33chrome: 20/20 iterations passed.

• Removed the temporary Shampoo rule and reran testUSBankAccountLiteSuccess plus testUSBankAccountLiteCancelAllowsUserToContinue: 2/2 tests passed.

• git diff --check

Screenshots

Before	After
Not applicable; test infrastructure only.	Not applicable; test infrastructure only.

Changelog

Not applicable; this only changes Android test infrastructure.

[amk-stripe]

From motivation:

The Financial Connections frontend flag bank_connections_enable_select_institution_first controls whether institution-default or agree-button is rendered first.

Instead of having special logic to handle either coming first, should the test itself specify which to wait for first based on that front end flag? Or maybe we should just make the tests deterministic rather than handling this flag being non-deterministic

[jaynewstrom-stripe]

According to codex:

Server-owned bank_connections_enable_select_institution_first routing can place either pane first.

So I think this is right?

[amk-stripe]

Ah I see, I was misled by it being called a "frontend flag", I thought it was on the client. Seems ok then, though still unfortunate that we can't just have a deterministic environment for our tests to run in

[amk-stripe]

Approving because the webview timeouts seem good to have but I'm worried we're just obscuring a real issue in the tests rather than fixing it, regarding the non-determinism of which button appears first in the webview