How to Pass Parameters to a Pester Test Script

• Windows PowerShell
• Pester

Applies to Pester 3.4.0

Like any Windows PowerShell script, a script that contains Pester tests can include parameters. It’s easy enough to run the script and pass parameters and values in the usual way.

But, when you use Invoke-Pester to run the script, you need to pass the parameters in a hash table. This blog explains how to do it.

This post is the third in a series about how to run Pester tests. See also, How to Run a Pester Test and Invoke-Pester: Running Selected Tests.

See the posts in this Pester series:

• How to Run a Pester Test
• Invoke-Pester: Running Selected Tests
• How to Pass Parameters to a Pester Test Script
• Testing Pester Code Coverage

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To use Invoke-Pester to pass parameters to a script, use a command like this one:

Invoke-Pester -Script @{Path='C:\Tests\MyTests.Tests.ps1';Parameters=@{Name='Pester';Version='3.4.0'}}

Or, this one:

Invoke-Pester -Script @{Path = 'C:\Tests\MyTests.Tests.ps1'; Arguments = 'Pester', '3.4.0'}

The Script parameter of Invoke-Pester typically takes a array of paths, either paths to a directory or to scripts that typically contain Pester tests, or both.

But, it can also take a hash table. One hint is that Script parameter type is [System.Object[]], not [System.String[]].

Here are hash table keys:

• Path (required) <string>: The value of the Path key must be a single string, presumably (but not required) the path to directories or files. Wildcards are supported. A hash table with only the Path key is equivalent to submitting a string value to the Script parameter, except that this key is limited to one string.

  Invoke-Pester -Script @{Path='C:\Tests\MyTests.Tests.ps1'}

• Parameters <hashtable>:  Each key-value pair in the (nested) hash table consists of a parameter name and its value, such as @{ComputerName = ‘localhost’}. Use this key to pass named parameter names and values to a script.

  Invoke-Pester -Script @{Path = 'C:\Tests\MyTests.Tests.ps1'; Parameters = @{Name = 'Pester'; Version = '3.4.0'}}

• Arguments <array>: Use this key to pass positional parameter values to a script, such as ‘localhost’, $true or @(‘localhost’, $true).

  Invoke-Pester -Script @{Path = 'C:\Tests\MyTests.Tests.ps1'; Arguments = 'Pester', '3.4.0'}

Invoke-Pester splats the parameters and arguments to the scripts as it calls them.

Typically, the Path value in the hash table resolves to a particular script that takes the specified named and/or positional parameters. But, when you pass parameters to a script that has no parameters, the extraneous parameters are ignored, so you can use a directory value effectively.

For example, this command passes the ComputerName to one .Tests.ps1 file, but the command runs all .Tests.ps1 files in the directory and its subdirectories.

Invoke-Pester -Script @{Path = 'C:\Tests\MyTests'; Parameters = @{ComputerName = 'localhost'}}

Of course, this strategy is error-prone and will not work when more than one of the scripts being run takes different parameters, so it’s probably not advisable.

But, it’s easy enough to pass parameters to a Pester test. Pester really is amazing!

Learning Pester? Check out Real-World Test-Driven Development with Pester. The code and slides are in Github at https://github.com/juneb/PesterTDD.

June Blender is a technology evangelist at SAPIEN Technologies, Inc. You can reach her at This email address is being protected from spambots. You need JavaScript enabled to view it. or follow her on Twitter at @juneb_get_help.

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