How do I mock Read-Host in a Pester test?

Question

If i have this function:

Function Test-Foo {

    $filePath = Read-Host "Tell me a file path"
}

How do i mock the Read-Host to return what i want? e.g. I want to do something like this (which doesn't work):

Describe "Test-Foo" {
  Context "When something" {
        Mock Read-Host {return "c:\example"}

        $result = Test-Foo

        It "Returns correct result" {
            $result | Should Be "c:\example"
        }
    }
}

Bert Levrau · Accepted Answer · 2017-01-05T10:38:43.420

7

This behavior is correct:

you should change you're code to

Import-Module -Name "c:\LocationOfModules\Pester"

Function Test-Foo {
    $filePath = Read-Host "Tell me a file path"
    $filePath
}

Describe "Test-Foo" {
  Context "When something" {
        Mock Read-Host {return "c:\example"}

        $result = Test-Foo

        It "Returns correct result" { # should work
            $result | Should Be "c:\example"
        }
         It "Returns correct result" { # should not work
            $result | Should Be "SomeThingWrong"
        }
    }
}

edited Jan 05 '17 at 10:38

answered Dec 22 '16 at 14:33

Bert Levrau

975
8
11

When i run it it still hangs on the Read-Host line though? `PS D:\Temp\Scrap> invoke-pester Describing Test-Foo Context When something Tell me a file path:` – Pete Whitehead Jan 05 '17 at 10:00
I have changed the example, Can you please try to coppy this to a new ps1 and test if you have the desired result? – Bert Levrau Jan 05 '17 at 10:31
That does work! In my test I have the function I want to test in a separate psm1 file. I must be importing it wrong. Thanks a lot! – Pete Whitehead Jan 05 '17 at 11:15
1

This example does not currently work for me in Pester v5 – Zam Aug 12 '21 at 19:56
The `Mock` statement is contextual on Pester v5. You can move the `Mock` statement into `BeforeAll {}` section within the `Describe {}` section, or into the same `It {}` section where you use `Read-Host`. – zionyx Sep 16 '21 at 13:04

zionyx · Answer 2 · 2021-09-16T13:21:37.193

An extension to Bert's answer, this is the updated code sample for Pester v5.

The difference from Pester v4 is that Mocks are scoped based on their placement.

Function Test-Foo {
    $filePath = Read-Host "Tell me a file path"
    $filePath
}

Describe "Test-Foo" {

    BeforeAll {
        # Variables placed here is accessible by all Context sections.
        $returnText = "c:\example"
    }

    Context "When something" {

        BeforeAll {
            # You can mock here so every It gets to use this mock
            Mock Read-Host {return $returnText}
        }

        It "Returns correct result" {
            # Place mock codes here for the current It context
            # Mock Read-Host {return $returnText}

            $result = Test-Foo
            $result | Should Be $returnText
        }
    }
}

How do I mock Read-Host in a Pester test?

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