Yester

Yester is a Pester wrapper for executing tests defined in YAML. The goal of this is project is to enable simple, repeatable tests for infrastructure engineers with little understanding or want to learn PowerShell and Pester. Yester only requires a basic understanding of YAML to compose tests.

Installation

Yester depends on Pester and powershell-yaml

At this point in time, Yester only exists on GitHub, so you will need to install Yester from this repository. However, I may eventually publish it to the PowerShell Gallery.

To locate a suitable module path, see $Env:PSModulePath.

Usage

The Invoke-Yester commandlet will execute the tests identified using the -Path parameter.

Invoke-Yester -Path .\my-tests.yml

You can also load multiple YAML test files by specifying a folder containing one or more YAML files with a .yml or .yaml extension.

Invoke-Yester -Path .\my-tests\

The resulting output should be familiar.

Describing Example Yester Configuration Test

  Context Yester Environment
    [+] We should be using the console 33ms
  [+] 10 should not be greater than 100 2ms

YAML Specification

Each YAML file represents a single Describe block. The Describe and Name keys at the root must be defined.

Name: This is the description for the Describe block
Describe:

Optionally, one or more Context blocks can be defined.

Name: This is the description for the Describe block
Describe:
  Context:
    - Name: Context Block 1
      It:
        ...
    - Name: Context Block 2
      It:
      ...

As you would expect, you can make multiple asserts in a given context. For an assertion, all keys are required.

Name: This is the description for the Describe block
Describe:
  Context:
    - Name: Context Block 1
      It:
        - Name: 10 should not be greater than 100
	  Left: 10
	  Right: 100
	  Operator: -Not -BeGreaterThan

This configuration is the same as the expression $Left | Should -Not -BeGreater than $Right or 10 | Should -Not -BeGreaterThan 100 when expanded.

Of course, expressions are also welcome.

Name: This is the description for the Describe block
Describe:
  Context:
    - Name: Context Block 1
      It:
        - Name: We should be using the console
	  Left: (Get-Host).Console
	  Right: Console
	  Operator: -Be

Finally, Invoke-Expression is used to execute the actual Pester tests. If Left or Right is evaluated to $null by Invoke-Expression, the value is treated as a string.