Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: all files reviewed, 4 unresolved discussions (waiting on @IAMJDA)

source/Classes/020.SqlPermission.ps1 line 373 at r1 (raw file):

            New-InvalidOperationException -Message $missingPrincipalMessage
        }

We should not need this check at all since it is already evaluated in the Set-SqlDscServerPermission command. I rather see this change for the resource SqlPermission in a separate PR as we also need integration tests. Please revert the changes for this file and move it to a separate PR. 🙂

Code quote:

        $testSqlDscIsPrincipalParameters = @{
            ServerObject      = $serverObject
            Name              = $this.Name
        }

        # This will test wether the principal exist.
        $isLogin = Test-SqlDscIsLogin @testSqlDscIsPrincipalParameters
        $isRole = Test-SqlDscIsRole @testSqlDscIsPrincipalParameters

        if (-not $isLogin -and -not $isRole)
        {
            $missingPrincipalMessage = $this.localizedData.NameIsMissing -f @(
                $this.Name,
                $this.InstanceName
            )

            New-InvalidOperationException -Message $missingPrincipalMessage
        }

source/Public/Set-SqlDscServerPermission.ps1 line 107 at r1 (raw file):

        if (-not $isLogin -and -not $isRole)
        {
            $missingPrincipalMessage = $script:localizedData.ServerPermission_MissingPrincipal -f $Name, $ServerObject.InstanceName

We need to update the localized string

Code quote:

ServerPermission_MissingPrincipal

source/Public/Set-SqlDscServerPermission.ps1 line 117 at r1 (raw file):

                )
            )
            return

We should not need return here as we throw a terminating error?

Code quote:

return

tests/Unit/Public/Set-SqlDscServerPermission.Tests.ps1 line 430 at r1 (raw file):

                Mock -CommandName Test-SqlDscIsRole -MockWith {
                    return $false
                }

We should add a test that actually test the it is a role and not a login.

Code quote:

                Mock -CommandName Test-SqlDscIsRole -MockWith {
                    return $false
                }