Issue 320 fix?

functions/Get-DatabaseDiskFreeSpace.ps1

@@ -0,0 +1,116 @@
+function Get-DatabaseDiskFreeSpace {
+    <#
+    .SYNOPSIS
+        Returns if there is enough diskspace for the instance to grow for one cycle.
+
+    .DESCRIPTION
+        Returns if there is enough diskspace for the instance to grow for one cycle.
+        The checks is disk based, so the check will be done for each disk where the databases stores files.
+
+    .NOTES
+        Tags: Database, FileSize, FileGrowth
+        Author: Reitse Eskens (@2meterDBA)
+
+    .PARAMETER SqlInstance
+        The Instance for which you want to perform your check
+
+    .PARAMETER SqlCredential
+        Credentials to connect to the SQL Server instance if the calling user doesn't have permission
+
+    .EXAMPLE
+        Get-DatabaseDiskFreeSpace -SqlInstance sql2016
+    #>
+
+[CmdletBinding()]
+
+param (
+        [parameter(ValueFromPipeline)]
+        [DbaInstanceParameter[]]$SqlInstance,
+        [PSCredential]$SqlCredential
+       )
+
+
+begin {
+<#
+    Step one. Get the free diskspace from the disks where Sql Server is parking it's files.
+    The line will get the data from the chosen instance. Next the result is filtered down to just the drive letter for the summation later on.
+    The -unique is used to limit the results. We get a result line for each database file, but all we need is a drive and the free space.
+
+#>
+try {
+    $DiskFreeSpace = Get-DbaDbFile -SqlInstance $SqlInstance | Select-Object @{label='DriveLetter';Expression={$_.PhysicalName.substring(0,3)}}, VolumeFreeSpace, @{label='ComputerName';Expression={$env:COMPUTERNAME}} |Sort-Object -Property Driveletter -Unique
+}
+catch {
+    Stop-PSFFunction -Message "There was a problem getting the free diskspace" -ErrorRecord $psitem
+}
+#finally {
+#        Write-PSFMessage -Level Warning -Message "Execution was cancelled!"
+#        Pop-Location
+#}
+<#
+    Step two. Determine per drive letter how much growth can be expected.
+    Same concept as the first step, but now we're looking at the file growth.
+#>
+
+try {
+    $FileGrowth = Get-DbaDbFile -SqlInstance $SqlInstance | Select-Object @{label='DriveLetter';Expression={$_.PhysicalName.substring(0,3)}}, NextGrowthEventSize
+}
+catch {
+    Stop-PSFFunction -Message "There was a problem getting the disk growth data" -ErrorRecord $psitem
+}
+#finally {
+#        Write-PSFMessage -Level Warning -Message "Execution was cancelled!"
+#        Pop-Location
+#}
+<#
+    Step three, summation of the disk growth
+#>
+
+
+$calc = $FileGrowth | Group-Object -Property Driveletter | ForEach-Object -Process {
+    $Sum = $_.group | Measure-Object -Sum -Property NextGrowthEventSize
+    [pscustomobject]@{DriveLetter=$_.Name ; Value = [SqlCollaborative.Dbatools.Utility.Size]::new($Sum.sum)}
+}
+
+<#
+    Step three and a bit, because the summation results in something else than GB, the result is rebuilt to gigabytes 
+#>
+
+
+# $CalcInGB = $calc | Select-Object DriveLetter, @{name="GrowthInGB" ; Expression={[math]::Round($_.value/1GB, 2)}}
+# The above step is still alive for regression testing. 
+<#
+    Now for the interesting part. Time to compare the results!
+    For each line in the disk free space results, the expected growth will be checked.
+    If the drives are the same, the comparison will take place and the result will be shown.   
+#>
+
+
+$DiskFreeSpace | ForEach-Object -Process {
+    if($_.DriveLetter -cin $Calc.DriveLetter)
+    {
+        $localDisk = $_.DriveLetter
+        $localFileSize = $_.VolumeFreeSpace
+        $computerName = $_.ComputerName
+        $Calc | ForEach-Object -Process {
+            If($_.DriveLetter -eq $localDisk)
+            {
+                if($_.GrowthInGB -ge  $localFileSize )
+                {
+                    [PSCustomObject]@{Computer = $computerName ; SQLInstance = $SqlInstance ; DiskFreeSpace = $localFileSize ; Growth = $_.Value ; GrowthAchievable = 'false'} 
+                }
+                else
+                {
+                    [PSCustomObject]@{Computer = $computerName ; SQLInstance = $SqlInstance ; DiskFreeSpace = $localFileSize ; Growth = $_.Value ; GrowthAchievable = 'true'}
+                }
+
+            }
+          }
+    }
+    else
+    {
+        Write-Host $_.DriveLetter 'Pike! You stupid Boy!'
+    }
+   }
+  }
+}

internal/assertions/Instance.Assertions.ps1

@@ -91,6 +91,12 @@ function Assert-TempDBSize {
     @((Get-DbaDbFile -SqlInstance $Instance -Database tempdb).Where{$_.Type -eq 0}.Size.Megabyte |Select-Object -Unique).Count | Should -Be 1 -Because "We want all the tempdb data files to be the same size - See https://blogs.sentryone.com/aaronbertrand/sql-server-2016-tempdb-fixes/ and https://www.brentozar.com/blitz/tempdb-data-files/ for more information"
 }
 
+function Assert-DBGrowthEvent {
+    Param($Instance)
+
+    (Get-DatabaseDiskFreeSpace -SqlInstance $Instance).Where{$_.GrowthAchievable -eq 'true'} | Should -Be 'true' -Because "We want enough space to let all the databases grow at least once more."
+}
+
 function Assert-InstanceSupportedBuild {
     Param(
         [string]$Instance,