Test JSON narrowing

packages/cli-kit/src/public/common/ts/json-narrowing.test.ts

@@ -0,0 +1,15 @@
+import {assertStringMap} from './json-narrowing.js'
+import {BugError} from '@shopify/cli-kit/node/error'
+import {describe, expect, test} from 'vitest'
+
+describe('json-narrowing', () => {
+  test('assertStringMap', () => {
+    assertStringMap({yes: 'please'})
+  })
+  test('assertStringMap fails on null', () => {
+    expect(() => assertStringMap(null)).toThrow(BugError)
+  })
+  test('assertStringMap fails on non-object', () => {
+    expect(() => assertStringMap('hello')).toThrow(BugError)
+  })
+})