如何使用 RSpec 测试 `rand()`? [英] How do I test `rand()` with RSpec?

问题描述

我有一个方法可以做这样的事情:

I have a method that does something like this:

def some_method
  chance = rand(4)
  if chance == 1 do
    # logic here
  else
    # another logic here
  end
end

当我使用 RSpec 测试这个方法时，里面的 rand(4) 总是生成 0.我不是在测试 Rails 的 rand 方法，我是在测试我的方法.测试我的方法的常见做法是什么?

When I use RSpec to test this method, rand(4) inside it always generates 0. I am not testing rand method of Rails, I am testing my method. What is a common practice to test my method?

推荐答案

我会考虑两种方法:

方法 1:

在 before :each 块中使用 srand( seed ) 中的已知种子值:

Use a known value of seed in srand( seed ) in a before :each block:

before :each do
  srand(67809)
end

这适用于 Ruby 版本，并在您想要涵盖特定组合时为您提供控制权.我经常使用这种方法 - 仔细想想，那是因为我正在测试的代码主要使用 rand() 作为数据源，其次(如果有的话)用于分支.它也被大量调用，因此对返回值进行逐个调用控制会适得其反，我最终会在大量看起来随机"的测试数据中进行铲除，可能首先通过调用生成它 <代码>rand()!

This works across Ruby versions, and gives you control in case you want to cover particular combinations. I use this approach a lot - thinking about it, that's because the code I was testing uses rand() primarily as a data source, and only secondarily (if at all) for branching. Also it gets called a lot, so exerting call-by-call control over returned values would be counter-productive, I would end up shovelling in lots of test data that "looked random", probably generating it in the first place by calling rand()!

您可能希望在至少一个测试场景中多次调用您的方法，以确保您拥有合理的组合覆盖率.

You may wish to call your method multiple times in at least one test scenario to ensure you have reasonable coverage of combinations.

方法 2:

如果由于 rand() 输出的值而有分支点，并且断言是如果它选择 X，那么 Y 应该发生"的类型，那么它也是合理的测试套件模拟 rand( n ) 并返回您想要断言的值:

If you have branch points due to values output from rand() and your assertions are of the type "if it chooses X, then Y should happen", then it is also reasonable in the same test suite to mock out rand( n ) with something that returns the values you want to make assertions about:

 require 'mocha/setup'

 Kernel.expects(:rand).with(4).returns(1)
 # Now run your test of specific branch

本质上，这些都是白盒"测试方法，它们都要求您知道您的例程在内部使用 rand().

In essence these are both "white box" test approaches, they both require you to know that your routine uses rand() internally.

黑盒"测试要困难得多 - 您需要断言行为在统计上是正确的，并且您还需要接受非常广泛的可能性，因为有效的随机行为可能导致幻像测试失败.

A "black box" test is much harder - you would need to assert that behaviour is statistically OK, and you would also need to accept a very wide range of possibilities since valid random behaviour could cause phantom test failures.

这篇关于如何使用 RSpec 测试 `rand()`?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！