E2E: leave no navigation in flight when authenticate() returns

Calypso home hands a logged-in user over to the Dashboard on another host,
and that navigation starts after the load event. A spec that authenticates
with waitUntilStable false and navigates straight away raced it and lost:
reader__view failed both its attempts on both devices with ERR_ABORTED on
the goto to /reader, with the Dashboard shell on screen.

The prime-logins project hid this. It logged in as the account before the
suite, so by the time the spec ran the container had served the same pages
already and the hand-over fired earlier than the spec's own navigation.

Such a caller navigates itself next, so authenticate() no longer loads
Calypso home for it, and it waits for the URL to stop changing before it
returns.

Author: lucatume

packages/calypso-e2e/src/lib/test-account.ts

@@ -21,6 +21,8 @@ const LOCK_STALE_MS = 90 * 1000;
 const LOCK_WAIT_MS = 60 * 1000;
 const LOCK_POLL_MS = 500;
 const LOGIN_ATTEMPTS = 2;
+const SETTLE_POLL_MS = 500;
+const SETTLE_TIMEOUT_MS = 10 * 1000;
 
 /**
  * Creates a directory, reporting whether this call is the one that created it.
@@ -39,6 +41,30 @@ async function createdDirectory( dirPath: string ): Promise< boolean > {
 	}
 }
 
+/**
+ * Waits until the page stops navigating on its own.
+ *
+ * Calypso home hands a logged-in user over to the Dashboard, which lives on another host, and
+ * that navigation starts after the load event. Handing back a page with it still in flight
+ * aborts whatever the caller navigates to next.
+ *
+ * @param {Page} page Page to watch.
+ */
+async function waitForNavigationToSettle( page: Page ): Promise< void > {
+	// Polls the URL rather than waiting for a named destination: where a logged-in user lands
+	// is the app's business and has changed before.
+	const deadline = Date.now() + SETTLE_TIMEOUT_MS;
+	let url = page.url();
+
+	while ( Date.now() < deadline ) {
+		await sleep( SETTLE_POLL_MS );
+		if ( page.url() === url ) {
+			return;
+		}
+		url = page.url();
+	}
+}
+
 /**
  * Represents the WPCOM test account.
  */
@@ -79,11 +105,16 @@ export class TestAccount {
 		{ url, waitUntilStable = true }: { url?: string | RegExp; waitUntilStable?: boolean } = {}
 	): Promise< void > {
 		const browserContext = page.context();
+		// A caller that asks for neither a URL nor stability navigates itself next, so landing
+		// on Calypso home first only buys a redirect that competes with that navigation.
+		const landOnCalypsoHome = Boolean( url ) || waitUntilStable;
 
 		if ( ! ( await this.logInOncePerRun( page ) ) ) {
 			await browserContext.clearCookies();
 			await browserContext.addCookies( await this.getAuthCookies() );
-			await page.goto( getCalypsoURL( '/' ) );
+			if ( landOnCalypsoHome ) {
+				await page.goto( getCalypsoURL( '/' ) );
+			}
 		}
 
 		if ( url ) {
@@ -92,6 +123,8 @@ export class TestAccount {
 		if ( waitUntilStable ) {
 			const sidebarComponent = new SidebarComponent( page );
 			await sidebarComponent.waitForSidebarInitialization();
+		} else {
+			await waitForNavigationToSettle( page );
 		}
 	}