在单元测试中处理DateTime.Now的策略 [英] Strategies for dealing with DateTime.Now in unit tests

问题描述

我的业务逻辑在星期六或星期日不执行某些功能。我希望我的单元测试能够验证是否执行了这些功能，但是测试将在周六/周日失败。

I have business logic that does not perform certain functions on Saturday or Sunday. I want my unit tests to verify that these functions are performed, but the tests will fail on Saturday/Sunday.

我认为最简单的方法是传递单元测试友好的消息，指出如果在星期六/星期日运行测试结果，则该测试结果无效。

I figure the easiest route is to have the unit tests convey a friendly message stating that the test results are not valid if they are run on Saturday/Sunday.

使用C＃/ NUnit ...

With C# / NUnit...

Assert.That(
  DateTime.Now.DayOfWeek != DayOfWeek.Sunday && DateTime.Now.DayOfWeek !=      
  DayOfWeek.Saturday, "This test cannot be run on Saturday or Sunday");

是否可以/建议尝试模拟日期？

Is it possible/advisable to try and mock the date? Are there other strategies for handling this scenario?

推荐答案

是否有可能/建议尝试模拟？日期？

Is it possible/advisable to try and mock the date?

是的，不仅建议这样做，而且还是唯一可靠地对代码进行单元测试的方法。假设您想测试以下（无意义的）方法：

Yes, not only that it is advisable but it is the only way to reliably unit test your code in isolation. Suppose that you wanted to test the following (meaningless) method:

public bool Foo()
{
    return (DateTime.Now.DayOfWeek == DayOfWeek.Sunday);
}

很明显您无法测试它，因为它依赖于静态方法（更精确的是静态现在属性）。显然，像这样紧密耦合的组件不能单独进行单元测试。

It's more than obvious that you can't test it because it relies on a static method (the static Now property to be more precise). It's clear that components which are tightly coupled like this cannot be unit tested in isolation.

现在考虑这种改进（用构造函数DI分离关注点）：

Now consider this improvement (separation of concerns with constructor DI):

private readonly Func<DateTime> _nowProvider;
public SomeClass(Func<DateTime> nowProvider)
{
    _nowProvider = nowProvider;
}

public bool Foo()
{
    return (_nowProvider().DayOfWeek == DayOfWeek.Sunday);
}

现在，单元测试变得更好，更容易。 SomeClass 不再取决于不确定的日期。在实际的应用程序中，您显然会实例化 SomeClass ：

Now that's much better and easier to unit test. SomeClass no longer depends on a non-deterministic date. In the real application you would obviously instantiate SomeClass like this:

var s = new SomeClass(() => DateTime.Now);
s.Foo();

在单元测试中，您将对其进行模拟，以便可以验证两种情况：

and in your unit test you will mock it so that you can verify both cases:

var subjectUnderTest = new SomeClass(() => new DateTime(2011, 1, 3));
var actual = subjectUnderTest.Foo();
// assertions, ...

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