Pester 如何模拟模式 "test existence (not found) - create - test again to confirm creation" 中的 "test" 函数？

Question

下面是一些伪代码，显示了要测试的函数：

function Set-Something
{
    if (Test-Something)
    {
        return $True
    }

    # Not found so do something to create it.
    Do-Something

    # Check it's been created successfully.
    if (Test-Something)
    {
        return $True
    }

    return $False
}

这一定是一个相当常见的模式："Test for existence - if not found create - test again to verify creation"。测试大多数分支非常简单，但是如何测试第一次调用 Test-Something 失败，然后第二次调用成功的分支？

到目前为止，这是我的测试代码：

Describe 'Set-Something' {

    Context 'already exists' {
        Mock Test-Something { return $True }
        Mock Do-Something

        It 'returns True' {
            { Set-Something } | Should -Be $True
        }

        It 'does not call Do-Something' {
            Set-Something
            Assert-MockCalled Do-Something -Times 0 -Exactly
        }
    }

    Context 'does not already exist and creation fails' {
        Mock Test-Something { return $False }
        Mock Do-Something

        It 'calls Do-Something' {
            Set-Something
            Assert-MockCalled Do-Something -Times 1 -Exactly
        }

        It 'calls Test-Something twice' {
            Set-Something
            Assert-MockCalled Test-Something -Times 2 -Exactly
        }

        It 'returns False' {
            { Set-Something } | Should -Be $False
        }
    }

    Context 'does not already exist and creation succeeds' {
        Mock Test-Something { ?? }
        Mock Do-Something

        It 'calls Do-Something' {
            Set-Something
            Assert-MockCalled Do-Something -Times 1 -Exactly
        }

        It 'calls Test-Something twice' {
            Set-Something
            Assert-MockCalled Test-Something -Times 2 -Exactly
        }

        It 'returns True' {
            { Set-Something } | Should -Be $True
        }
    }
}

案例'does not already exist and creation succeeds'就是问题所在。 Test-Something 需要被模拟，所以它在第一次被调用时失败，第二次成功。传递给 Test-Something 的参数在每次调用中都是相同的，所以我不能使用 ParameterFilter 创建两个具有不同行为的 Test-Something 模拟。

Answer 1

我找到了几种模拟这个的方法：

1）使用一个"static"（即script-scoped）变量来记录状态

Context 'does not already exist and creation succeeds' {

    BeforeEach {
        $script:exists = $False
    }

    AfterAll {
        Remove-Variable exists -Scope Script
    }

    Mock Test-Something { 
        return $script:exists
    }

    Mock Do-Something {
        $script:exists = $True
    }

    It 'calls Do-Something' {
        Set-Something
        Assert-MockCalled Do-Something -Times 1 -Exactly
    }

    It 'calls Test-Something twice' {
        Set-Something
        Assert-MockCalled Test-Something -Times 2 -Exactly
    }

    It 'returns True' {
        { Set-Something } | Should -Be $True
    }
}

2) 使用散列table记录状态

Context 'does not already exist and creation succeeds' {

    BeforeEach {
        $mockState = @{
                        ItExists = $False    
                    }
    }

    Mock Test-Something { 
        return $mockState.ItExists
    }

    Mock Do-Something {
        $mockState.ItExists = $True
    }

    It 'calls Do-Something' {
        Set-Something
        Assert-MockCalled Do-Something -Times 1 -Exactly
    }

    It 'calls Test-Something twice' {
        Set-Something
        Assert-MockCalled Test-Something -Times 2 -Exactly
    }

    It 'returns True' {
        { Set-Something } | Should -Be $True
    }
}

就个人而言，我喜欢散列 table，因为在我看来 $mockState. ... 比 $script:... 更能表明变量的用途。此外，如果测试曾被并行化并且另一个 Describe 块修改了相同的变量，script-scoped 变量可能会导致竞争条件。

Pester 如何模拟模式 "test existence (not found) - create - test again to confirm creation" 中的 "test" 函数？

How can Pester mock the "test" function in the pattern "test existence (not found) - create - test again to confirm creation"?

powershell

unit-testing

pester