test(aws-amplify): add DefaultAmplify integration tests with real core singleton

Validates Storage preservation and setAuthConfig on reconfigure without mocking @aws-amplify/core.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ShrutiPundir17

packages/aws-amplify/__tests__/initSingleton.integration.test.ts

@@ -0,0 +1,123 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+/**
+ * Integration-style tests using the real @aws-amplify/core Amplify singleton
+ * (initSingleton.test.ts mocks core).
+ */
+import { Amplify as CoreAmplify, ResourcesConfig } from '@aws-amplify/core';
+
+import { cognitoUserPoolsTokenProvider } from '../src/auth/cognito';
+import { Amplify as DefaultAmplify } from '../src';
+
+const poolAConfig: ResourcesConfig = {
+	Auth: {
+		Cognito: {
+			userPoolClientId: 'client-a',
+			userPoolId: 'pool-a',
+		},
+	},
+};
+
+const poolBConfig: ResourcesConfig = {
+	Auth: {
+		Cognito: {
+			userPoolClientId: 'client-b',
+			userPoolId: 'pool-b',
+		},
+	},
+};
+
+const storageLibraryOptions = {
+	Storage: {
+		S3: {
+			defaultAccessLevel: 'private' as const,
+			isObjectLockEnabled: true,
+		},
+	},
+};
+
+describe('DefaultAmplify.configure integration', () => {
+	let setAuthConfigSpy: jest.SpyInstance;
+	let setKeyValueStorageSpy: jest.SpyInstance;
+
+	beforeEach(() => {
+		CoreAmplify.libraryOptions = {};
+		CoreAmplify.resourcesConfig = {};
+		setAuthConfigSpy = jest.spyOn(
+			cognitoUserPoolsTokenProvider,
+			'setAuthConfig',
+		);
+		setKeyValueStorageSpy = jest.spyOn(
+			cognitoUserPoolsTokenProvider,
+			'setKeyValueStorage',
+		);
+	});
+
+	afterEach(() => {
+		setAuthConfigSpy.mockRestore();
+		setKeyValueStorageSpy.mockRestore();
+		CoreAmplify.libraryOptions = {};
+		CoreAmplify.resourcesConfig = {};
+	});
+
+	it('keeps Storage and refreshes Cognito auth config on partial reconfigure', () => {
+		DefaultAmplify.configure(poolAConfig, storageLibraryOptions);
+
+		expect(CoreAmplify.libraryOptions.Storage).toEqual(
+			storageLibraryOptions.Storage,
+		);
+		expect(CoreAmplify.libraryOptions.Auth?.tokenProvider).toBe(
+			cognitoUserPoolsTokenProvider,
+		);
+		expect(setAuthConfigSpy).toHaveBeenCalledWith(poolAConfig.Auth);
+
+		setAuthConfigSpy.mockClear();
+
+		DefaultAmplify.configure(poolBConfig, { ssr: false });
+
+		expect(CoreAmplify.libraryOptions.Storage).toEqual(
+			storageLibraryOptions.Storage,
+		);
+		expect(CoreAmplify.getConfig().Auth?.Cognito?.userPoolClientId).toBe(
+			'client-b',
+		);
+		expect(setAuthConfigSpy).toHaveBeenCalledWith(poolBConfig.Auth);
+	});
+
+	it('merges prior libraryOptions when libraryOptions.Auth overrides default provider', () => {
+		DefaultAmplify.configure(poolAConfig, storageLibraryOptions);
+
+		setAuthConfigSpy.mockClear();
+
+		DefaultAmplify.configure(poolBConfig, {
+			Auth: {
+				tokenProvider: cognitoUserPoolsTokenProvider,
+				credentialsProvider:
+					CoreAmplify.libraryOptions.Auth!.credentialsProvider!,
+			},
+		});
+
+		expect(CoreAmplify.libraryOptions.Storage).toEqual(
+			storageLibraryOptions.Storage,
+		);
+		expect(setAuthConfigSpy).toHaveBeenCalledWith(poolBConfig.Auth);
+		expect(CoreAmplify.getConfig().Auth?.Cognito?.userPoolClientId).toBe(
+			'client-b',
+		);
+	});
+
+	it('syncs default Cognito auth config when only resource config is passed', () => {
+		DefaultAmplify.configure(poolAConfig, storageLibraryOptions);
+
+		setAuthConfigSpy.mockClear();
+
+		DefaultAmplify.configure(poolBConfig);
+
+		expect(CoreAmplify.libraryOptions.Storage).toEqual(
+			storageLibraryOptions.Storage,
+		);
+		expect(setAuthConfigSpy).toHaveBeenCalledWith(poolBConfig.Auth);
+		expect(CoreAmplify.getConfig().Auth?.Cognito?.userPoolId).toBe('pool-b');
+	});
+});