test(sanity): add toMatchEmissions matcher

packages/sanity/package.json

@@ -305,6 +305,7 @@
     "@types/semver": "^6.2.3",
     "@types/tar-fs": "^2.0.1",
     "@vitejs/plugin-react": "^4.3.4",
+    "@vitest/expect": "^3.0.5",
     "@vvo/tzdb": "6.137.0",
     "babel-plugin-react-compiler": "19.0.0-beta-714736e-20250131",
     "blob-polyfill": "^9.0.20240710",

packages/sanity/test/matchers/toMatchEmissions.ts

@@ -0,0 +1,49 @@
+import {type AsyncExpectationResult, type MatcherState} from '@vitest/expect'
+import {firstValueFrom, type OperatorFunction, Subject, toArray} from 'rxjs'
+
+export const NO_EMISSION = Symbol('NO_EMISSION')
+
+type Snapshot<A, B> = [A, B | typeof NO_EMISSION]
+
+interface OperatorFunctionMatchers<Type = unknown> {
+  /**
+   * Ensure each entry in the provided array results in the expected value being emitted when piped
+   * to the observable.
+   */
+  toMatchEmissions: Type extends () => OperatorFunction<infer A, infer B>
+    ? (snapshots: Snapshot<A, B>[]) => Promise<Type>
+    : never
+}
+
+declare module 'vitest' {
+  interface Assertion<T = any> extends OperatorFunctionMatchers<T> {}
+  interface AsymmetricMatchersContaining extends OperatorFunctionMatchers {}
+}
+
+export async function toMatchEmissions(
+  this: MatcherState,
+  createOperator: () => OperatorFunction<unknown, unknown>,
+  snapshots: [A: unknown, B: unknown][],
+): AsyncExpectationResult {
+  const {equals} = this
+  const input$ = new Subject()
+
+  const expectedEmissions = snapshots
+    .filter(([, expectedEmission]) => expectedEmission !== NO_EMISSION)
+    .map(([, expectedEmission]) => expectedEmission)
+
+  const emissions$ = input$.pipe(createOperator(), toArray())
+  const emissions = firstValueFrom(emissions$)
+
+  snapshots.forEach(([value]) => input$.next(value))
+  input$.complete()
+
+  const actualEmissions = await emissions
+
+  return {
+    pass: equals(actualEmissions, expectedEmissions),
+    message: () => 'Observable emissions did not match',
+    actual: actualEmissions,
+    expected: expectedEmissions,
+  }
+}

packages/sanity/test/setup/environment.ts

@@ -6,7 +6,13 @@ import './clipboardItemPolyfill'
 import '@testing-library/jest-dom/vitest'
 
 import {cleanup} from '@testing-library/react'
-import {afterEach, beforeEach, vi} from 'vitest'
+import {afterEach, beforeEach, expect, vi} from 'vitest'
+
+import {toMatchEmissions} from '../matchers/toMatchEmissions'
+
+expect.extend({
+  toMatchEmissions,
+})
 
 afterEach(() => cleanup())