Gets a list of all changesets from $Source branch that have not been merged into $Destination branch.

Get-TfsMergeCandidates.ps1

[System.Reflection.Assembly]::LoadWithPartialName("Microsoft.TeamFoundation.Client") | Out-Null

<#
.Synopsis
   Gets a list of all changesets from $Source that have not been merged into $Destination.
.DESCRIPTION
   Gets a list of all changesets from $Source that have not been merged into $Destination.
.EXAMPLE
   $tfs = Get-TfsServer http://<hostname>:8080/tfs
   Get-MergeCandidates -Server $tfs -Source "$/Some/Source/Branch" -Destination "$/Some/Destinsation/Branch"

   The Get-TfsServer cmdlet is included as part of the PowerShell snapin provided by the TFS Power Tools 
   extension for Visual Studio. If everything is installed correctly, you should be able to load the snapin
   with the following command:

   Add-PSSnapin Microsoft.TeamFoundation.PowerShell
#>
function Get-TfsMergeCandidates {
    [CmdletBinding()]
    Param(
        [Parameter(Mandatory = $true)]
        [Microsoft.TeamFoundation.Client.TfsTeamProjectCollection]
        $Server,

        [Parameter(Mandatory = $true)]
        [string]
        $Source,
        
        [Parameter(Mandatory = $true)]
        [string]
        $Destination
        
    )

    $service = $Server.GetService([Microsoft.TeamFoundation.VersionControl.Client.VersionControlServer])

    $candidates = $service.GetMergeCandidates(
        $Source, 
        $Destination, 
        [Microsoft.TeamFoundation.VersionControl.Client.RecursionType]::Full
    )

    $candidates | select -ExpandProperty changeset
}

Awesome work. Thank you.