feat(registration): add email domain whitelist policy

frontend/src/utils/__tests__/authError.spec.ts

@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest'
+import { buildAuthErrorMessage } from '@/utils/authError'
+
+describe('buildAuthErrorMessage', () => {
+  it('prefers response detail message when available', () => {
+    const message = buildAuthErrorMessage(
+      {
+        response: {
+          data: {
+            detail: 'detailed message',
+            message: 'plain message'
+          }
+        },
+      },
+      { fallback: 'fallback' }
+    )
+    expect(message).toBe('detailed message')
+  })
+
+  it('falls back to response message when detail is unavailable', () => {
+    const message = buildAuthErrorMessage(
+      {
+        response: {
+          data: {
+            message: 'plain message'
+          }
+        },
+      },
+      { fallback: 'fallback' }
+    )
+    expect(message).toBe('plain message')
+  })
+
+  it('falls back to error.message when response payload is unavailable', () => {
+    const message = buildAuthErrorMessage(
+      {
+        message: 'error message'
+      },
+      { fallback: 'fallback' }
+    )
+    expect(message).toBe('error message')
+  })
+
+  it('uses fallback when no message can be extracted', () => {
+    expect(buildAuthErrorMessage({}, { fallback: 'fallback' })).toBe('fallback')
+  })
+})