如何模拟使用不同参数和不同结果调用两次的命令

Question

我有一个要用 Pester 测试的 PowerShell 函数：

function Install-RequiredModule (
    [string]$ModuleName,
    [string]$RepositoryName,
    [string]$ProxyUrl
    )
{
    # Errors from Install-Module are non-terminating.  They won't be caught using  
    # try - catch.  So check $Error instead.
    # Clear errors so we know if one shows up it must have been due to Install-Module.
    $Error.Clear()

    # Want to fail silently, without displaying anything in console to scare the user, 
    # because it's valid for Install-Module to fail for a user behind a proxy server.
    Install-Module -Name $ModuleName -Repository $RepositoryName `
        -ErrorAction SilentlyContinue -WarningAction SilentlyContinue

    if ($Error.Count -eq 0)
    {
        # throw 'NO error'
        return
    }

    # There was an error so try again, this time with proxy details.

    $proxyCredential = Get-Credential -Message 'Please enter credentials for proxy server'

    # No need to Silently Continue this time.  We want to see the error details.
    $Error.Clear()

    Install-Module -Name $ModuleName -Repository $RepositoryName `
        -Proxy $ProxyUrl -ProxyCredential $proxyCredential

    if ($Error.Count -gt 0)
    {
        throw $Error[0]
    }

    if (-not (Get-InstalledModule -Name $ModuleName -ErrorAction SilentlyContinue))
    {
        throw "Unknown error installing module '$ModuleName' from repository '$RepositoryName'."
    }

    Write-Output "Module '$ModuleName' successfully installed from repository '$RepositoryName'."
}

这个函数可以调用Install-Module两次。它首先在没有代理凭据的情况下尝试，就好像它可以直接访问互联网一样。如果失败，它会再次尝试，这次使用代理凭据。

如何使用 Pester 测试此功能？

我在 PowerShell 论坛 here 上读到，我应该能够使用不同的参数筛选器模拟两次相同的命令。所以这就是我的尝试：

function ExecuteInstallRequiredModule ()
{
    Install-RequiredModule -ModuleName 'TestModule' -RepositoryName 'TestRepo' `
        -ProxyUrl 'http://myproxy'
}

Describe 'Install-RequiredModule' {

    $securePassword = "mypassword" | 
        ConvertTo-SecureString -asPlainText -Force
    $psCredential = New-Object System.Management.Automation.PSCredential  ('MyUserName', $securePassword)
    Mock Get-Credential { return $psCredential }

    # Want to add an error to $Error without it being written to the host.
    Mock Install-Module { Write-Error "Some error" -ErrorAction SilentlyContinue } `
        -ParameterFilter { $Name -eq  'TestModule' -and $Repository -eq 'TestRepo' -and $ErrorAction -eq 'SilentlyContinue' -and $WarningAction -eq 'SilentlyContinue'}
    Mock Install-Module { return $Null } `
        -ParameterFilter { $Name -eq  'TestModule' -and $Repository -eq 'TestRepo' -and $Proxy -eq 'http://myproxy' -and $ProxyCredential -eq $psCredential }

    Mock Get-InstalledModule { return @('Non-null text') }

    It 'attempts to install module a second time if first attempt fails' {
        ExecuteInstallRequiredModule
        #Assert-VerifiableMock
        #Assert-MockCalled Install-Module -Scope It -Times 2
    }
}

取消注释被测函数中显示 # throw 'NO error' 的行，我发现在第一次调用 Install-Module 后 $Error.Count 为 0。因此，在第二次调用 Install-Module 之前，不会调用正在创建非终止错误的模拟和函数 returns。

Answer 1

您可以在 try catch 循环中使用 -ErrorAction Stop 调用 install-module 命令。

try
{
    #run with no credentials
    Install-Module -Name $ModuleName -Repository $RepositoryName -ErrorAction stop -WarningAction SilentlyContinue
}
catch
{
    #when fails, run with proxy credentials
    Install-Module -Name $ModuleName -Repository $RepositoryName -Proxy $ProxyUrl -ProxyCredential $proxyCredential
}

您可以为同一个 try 命令设置多个 catch{} 块，以捕获不同类型的失败并执行您选择的脚本块。

Answer 2

问题似乎是 Pester 阻止了对公共参数的过滤，因此您对 'ErrorAction' 等的使用导致您的过滤器失败。

您可以在 Pester 模拟代码的第 254 行左右看到从模拟函数中删除的参数：Mock.ps1

此外，测试此删除是 Pester 自己的单元测试之一（第 283 行）：Mock.tests.ps1

Answer 3

对于处于类似情况的任何人，这是有效的测试的最终版本：

function Install-RequiredModule (
    [string]$ModuleName,
    [string]$RepositoryName,
    [string]$ProxyUrl
    )
{
    try
    {
        Install-Module -Name $ModuleName -Repository $RepositoryName `
            -ErrorAction Stop

        return
    }
    catch {}

    # There was an error so try again, this time with proxy details.

    $proxyCredential = Get-Credential -Message 'Please enter credentials for proxy server'

    # No need to Silently Continue this time.  We want to see the error details.
    $Error.Clear()

    Install-Module -Name $ModuleName -Repository $RepositoryName `
        -Proxy $ProxyUrl -ProxyCredential $proxyCredential

    if ($Error.Count -gt 0)
    {
        throw $Error[0]
    }

    if (-not (Get-InstalledModule -Name $ModuleName -ErrorAction SilentlyContinue))
    {
        throw "Unknown error installing module '$ModuleName' from repository '$RepositoryName'."
    }

    Write-Output "Module '$ModuleName' successfully installed from repository '$RepositoryName'."
}

#region Tests *************************************************************************************

function ExecuteInstallRequiredModule ()
{
    Install-RequiredModule -ModuleName 'TestModule' -RepositoryName 'TestRepo' `
        -ProxyUrl 'http://myproxy'
}

Describe 'Install-RequiredModule' {

    $securePassword = "mypassword" | 
        ConvertTo-SecureString -asPlainText -Force
    $psCredential = New-Object System.Management.Automation.PSCredential  ('MyUserName', $securePassword)
    Mock Get-Credential { return $psCredential }

    Mock Install-Module { Write-Error "Some error" }
    Mock Install-Module { return $Null } -ParameterFilter { $Proxy -ne $Null -and $ProxyCredential -ne $Null }

    Mock Get-InstalledModule { return @('Non-null text') }

    It 'attempts to install module a second time, with proxy, if first attempt fails' {
        ExecuteInstallRequiredModule  
        Assert-MockCalled Install-Module -Scope It -Times 2 -Exactly
    }
}

#endregion

如何模拟使用不同参数和不同结果调用两次的命令

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