Pester如何模拟“测试存在（未找到）-创建-再次测试以确认创建”模式中的“测试”功能？

Question

这是一些伪代码，显示要测试的功能：

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
}

这必须是一个相当普遍的模式：“测试是否存在-如果找不到，请创建-再次测试以验证创建”。 测试大多数分支非常简单，但是如何在第一次调用Test-Something失败然后第二次调用成功的地方测试分支呢？

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
        }
    }
}

问题是“尚不存在，创建成功”。 需要对Test-Something进行模拟，以便它在第一次调用时失败，而在第二次调用时成功。 传递给Test-Something的参数在每个调用中将是相同的，因此我不能使用ParameterFilter创建具有不同行为的Test-Something的两个模拟。

Answer 1

我发现了两种模拟方法：

1）使用“静态”（即脚本作用域）变量记录状态

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）使用哈希表记录状态

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
    }
}   

我个人喜欢哈希表，因为$mockState. ... $mockState. ...在我看来似乎比$script:...更能说明变量的用途。 同样，如果测试并行化并且另一个Describe块修改了相同的变量，则脚本范围的变量可能会导致竞争。