Increase code coverage (#22)

src/Helper/Get-RandomKey.ps1

@@ -32,6 +32,7 @@ function Get-RandomKey {
     [CmdletBinding()]
     param(
         [Parameter(Mandatory = $true)]
+        [ValidateNotNullOrEmpty()]
         [ValidateSet(16, 24, 32)]
         [string]$size
     )

src/Helper/Test-Module.ps1

@@ -83,14 +83,14 @@ Could not find the required {0} called {1}. Please install the required {0} to r
             }
 
             'PSSnapin' {
-                if (Get-PSSnapin -Name $Name -Registered) {
+                if (Get-PSSnapin -Name $Name -Registered -ErrorAction SilentlyContinue) {
                     return $true
                 }
                 else {
                     if ($StopIfFails) {
                         Write-Error -Message $Message -ErrorAction Stop -Category NotInstalled
-                        return $false
                     }
+                    return $false
                 }
             }