Add test for isNavigatingToNewRootLayout (#45305)

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Adds a test for isNavigatingToNewRootLayout.

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ]
[e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs)
tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

packages/next/src/client/components/router-reducer/is-navigating-to-new-root-layout.ts.test.ts

@@ -0,0 +1,100 @@
+import type { FlightRouterState } from '../../../server/app-render'
+import { isNavigatingToNewRootLayout } from './is-navigating-to-new-root-layout'
+
+describe('shouldHardNavigate', () => {
+  it('should return false if there is no new root layout', () => {
+    const getInitialRouterStateTree = (): FlightRouterState => [
+      '',
+      {
+        children: [
+          'linking',
+          {
+            children: ['', {}],
+          },
+        ],
+      },
+      undefined,
+      undefined,
+      true,
+    ]
+    const initialRouterStateTree = getInitialRouterStateTree()
+    const getNewRouterStateTree = (): FlightRouterState => {
+      return [
+        '',
+        {
+          children: [
+            'link-hard-push',
+            {
+              children: [
+                ['id', '456', 'd'],
+                {
+                  children: ['', {}],
+                },
+              ],
+            },
+          ],
+        },
+        null,
+        null,
+        true,
+      ]
+    }
+    const newRouterState = getNewRouterStateTree()
+
+    const result = isNavigatingToNewRootLayout(
+      newRouterState,
+      initialRouterStateTree
+    )
+
+    expect(result).toBe(false)
+  })
+
+  it('should return true if there is a mismatch between the root layouts', () => {
+    const getInitialRouterStateTree = (): FlightRouterState => [
+      '',
+      {
+        children: [
+          'linking',
+          {
+            children: ['', {}],
+          },
+          undefined,
+          undefined,
+          // Root layout at `linking` level.
+          true,
+        ],
+      },
+    ]
+    const initialRouterStateTree = getInitialRouterStateTree()
+    const getNewRouterStateTree = (): FlightRouterState => {
+      return [
+        '',
+        {
+          children: [
+            'link-hard-push',
+            {
+              children: [
+                ['id', '456', 'd'],
+                {
+                  children: ['', {}],
+                },
+              ],
+            },
+            null,
+            null,
+            // Root layout at `link-hard-push` level.
+            true,
+          ],
+        },
+      ]
+    }
+    const newRouterState = getNewRouterStateTree()
+
+    const result = isNavigatingToNewRootLayout(
+      newRouterState,
+      initialRouterStateTree
+    )
+
+    expect(result).toBe(true)
+  })
+})