unit-testing - 如何使用 `with-redefs` 始终从函数中抛出异常

Question

我想对代码的异常处理部分进行单元测试。为此，我使用 with-redefs 重新绑定(bind)可以抛出异常的 API，以便在测试期间抛出异常。我的测试函数看起来像这样

(deftest exception-handling
  (testing "Map exception to Ring-response map"
    (with-redefs [clj-http/get
                  (constantly (throw (ex-info "unexpected error" {:cause "A terrible calamity"})))]
      (is (= 500
        (:status
          (some-function-calling-http-get arg))))
    )
  )
)

运行 lein test 导致错误消息:

    ERROR in (exception-handling) (core.clj:4593)
Uncaught exception, not in assertion.
expected: nil
  actual: clojure.lang.ExceptionInfo: unexpected error
 at clojure.core$ex_info.invoke (core.clj:4593)

使用 (constantly (throw... in with-redefs 或只是断言异常被抛出 thrown? 也会导致同样的错误。

本质上，我正在寻找 constantly 的宏版本。

Answer 1

constantly 是函数，不是宏，所以 (constantly (throw ...)) 会立即抛出错误。

如果你想要一个每次调用都会抛出错误的函数，你需要这样的东西:

(with-redefs [clj-http/get (fn [& _] (throw (ex-info "unexpected error"
                                                     {:cause "A terrible calamity"})))]
  ...)