A simple Compare-Hashtable function for powershell

Compare-Hashtable.ps1

$ErrorActionPreference = "Stop"

function Compare-Hashtable {
<#
.SYNOPSIS
Compare two Hashtable and returns an array of differences.

.DESCRIPTION
The Compare-Hashtable function computes differences between two Hashtables. Results are returned as
an array of objects with the properties: "key" (the name of the key that caused a difference), 
"side" (one of "<=", "!=" or "=>"), "lvalue" an "rvalue" (resp. the left and right value 
associated with the key).

.PARAMETER left 
The left hand side Hashtable to compare.

.PARAMETER right 
The right hand side Hashtable to compare.

.EXAMPLE

Returns a difference for ("3 <="), c (3 "!=" 4) and e ("=>" 5).

Compare-Hashtable @{ a = 1; b = 2; c = 3 } @{ b = 2; c = 4; e = 5}

.EXAMPLE 

Returns a difference for a ("3 <="), c (3 "!=" 4), e ("=>" 5) and g (6 "<=").

$left = @{ a = 1; b = 2; c = 3; f = $Null; g = 6 }
$right = @{ b = 2; c = 4; e = 5; f = $Null; g = $Null }

Compare-Hashtable $left $right

#>	
[CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]
        [Hashtable]$Left,

        [Parameter(Mandatory = $true)]
        [Hashtable]$Right,

        [Parameter(Mandatory = $false)]
        [switch]$includeEqual	
	)
	
	function New-Result($Key, $LValue, $Side, $RValue) {
		New-Object -Type PSObject -Property @{
					key    = $Key
					lvalue = $LValue
					rvalue = $RValue
					side   = $Side
			}
	}
	[Object[]]$Results = $Left.Keys | % {
		if ($Left.ContainsKey($_) -and !$Right.ContainsKey($_)) {
			New-Result $_ $Left[$_] "<=" $Null
		} else {
			$LValue, $RValue = $Left[$_], $Right[$_]
			if ($LValue -ne $RValue) {
				New-Result $_ $LValue "!=" $RValue
			}
	        	elseif($includeEqual)
		    	{
				New-Result $_ $LValue "==" $RValue
		    	}
		}
	}
	$Results += $Right.Keys | % {
		if (!$Left.ContainsKey($_) -and $Right.ContainsKey($_)) {
			New-Result $_ $Null "=>" $Right[$_]
		} 
	}
	$Results 
}

Compare-Hashtable.Tests.ps1

$here = Split-Path -Parent $MyInvocation.MyCommand.Path
$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path) -replace '\.Tests\.', '.'
. "$here\$sut"

Describe "Compare-Hashtable" {
  Context "When both are empty" {
    $Left, $Right = @{}, @{}

    It "should return nothing" {
      Compare-Hashtable $Left $Right | Should BeNullOrEmpty
    }
  }
  
  Context "When both have one identical entry" {
    $Left, $Right = @{ a = "x" }, @{ a = "x" }

    It "should return nothing" {
      Compare-Hashtable $Left $Right | Should BeNullOrEmpty
    }
  }

  Context "When left contains a key with a null value" {
    $Left, $Right = @{ a = $Null }, @{}

    It "should return nothing" {
      [Object[]]$result = Compare-Hashtable $Left $Right

	    $result.Length | Should Be 1
	    $result.side   | Should Be "<="
	    $result.lvalue | Should Be $Null
	    $result.rvalue | Should Be $Null
    }
  }  

  Context "When right contains a key with a null value" {
    $Left, $Right = @{}, @{ a = $Null }

    It "should return nothing" {
      [Object[]]$result = Compare-Hashtable $Left $Right

	    $result.Length | Should Be 1
	    $result.side   | Should Be "=>"
	    $result.lvalue | Should Be $Null
	    $result.rvalue | Should Be $Null
    }
  }  
  
  Context "When both contain various stuff " {
    $Left = @{ a = 1; b = 2; c = 3; f = $Null; g = 6; k = $Null }
    $Right = @{ b = 2; c = 4; e = 5; f = $Null; g = $Null; k = 7 }
    $Result = Compare-Hashtable $Left $Right

    It "should contain 5 differences" {
      $Result.Length | Should Be 5
    }
    It "should return a: 1 <=" {
      ($Result | ? { $_.Key -eq "a" }).Side   | Should Be "<="  
      ($Result | ? { $_.Key -eq "a" }).LValue | Should Be 1  
      ($Result | ? { $_.Key -eq "a" }).RValue | Should Be $Null  
    }
    It "should return c: 3 <= 4" {
      ($Result | ? { $_.Key -eq "c" }).Side   | Should Be "!="  
      ($Result | ? { $_.Key -eq "c" }).LValue | Should Be 3  
      ($Result | ? { $_.Key -eq "c" }).RValue | Should Be 4  
    }
    It "should return e: <= 5" {
      ($Result | ? { $_.Key -eq "e" }).Side   | Should Be "=>"  
      ($Result | ? { $_.Key -eq "e" }).LValue | Should Be $Null  
      ($Result | ? { $_.Key -eq "e" }).RValue | Should Be 5  
    }
    It "should return g: 6 !=" {
      ($Result | ? { $_.Key -eq "g" }).Side   | Should Be "!="  
      ($Result | ? { $_.Key -eq "g" }).LValue | Should Be 6  
      ($Result | ? { $_.Key -eq "g" }).RValue | Should Be $Null  
    }
    It "should return k: != 7" {
      ($Result | ? { $_.Key -eq "k" }).Side   | Should Be "!="  
      ($Result | ? { $_.Key -eq "k" }).LValue | Should Be $Null  
      ($Result | ? { $_.Key -eq "k" }).RValue | Should Be 7  
    }       
  } 
}