Add extra tests

packages/backend-core/src/users/test/db.spec.ts

@@ -38,6 +38,7 @@ describe("UserDB", () => {
       email,
       tenantId: config.getTenantId(),
     })
+
     await config.doInTenant(async () => {
       const saveUserResponse = await db.save(user)
 
@@ -53,4 +54,18 @@ describe("UserDB", () => {
       })
     })
   })
+
+  it("the same email cannot be used twice in the same tenant", async () => {
+    const email = generator.email({})
+    const user: User = structures.users.user({
+      email,
+      tenantId: config.getTenantId(),
+    })
+
+    await config.doInTenant(() => db.save(user))
+
+    await config.doInTenant(() =>
+      expect(db.save(user)).rejects.toThrow(`Email already in use: '${email}'`)
+    )
+  })
 })