[Ubuntu] Migrate Toolset tests to Pester (#2339)

* migrate toolset tests to pester

* move test invocation

* minor fixes

images/linux/scripts/tests/Toolset.Tests.ps1

@@ -0,0 +1,62 @@
+Describe "Toolset" {
+    $tools = (Get-ToolsetContent).toolcache
+
+    $toolsExecutables = @{
+        Python = @{
+            tools = @("python", "bin/pip")
+            command = "--version"
+        }
+        node = @{
+            tools = @("bin/node", "bin/npm")
+            command = "--version"
+        }
+        PyPy = @{
+            tools = @("bin/python", "bin/pip")
+            command = "--version"
+        }
+        go = @{
+            tools = @("bin/go")
+            command = "version"
+        }
+        Ruby = @{
+            tools = @("bin/ruby")
+            command = "--version"
+        }
+    }
+
+    foreach($tool in $tools) {
+        $toolName = $tool.Name
+        Context "$toolName" {
+            $toolExecs = $toolsExecutables[$toolName]
+
+            foreach ($version in $tool.versions) {
+                # Add wildcard if missing
+                if ($version.Split(".").Length -lt 3) {
+                    $version += ".*"
+                }
+
+                $expectedVersionPath = Join-Path $env:AGENT_TOOLSDIRECTORY $toolName $version
+
+                It "$version version folder exists" -TestCases @{ ExpectedVersionPath = $expectedVersionPath} {
+                    $ExpectedVersionPath | Should -Exist
+                }
+
+                $toolExecs = $toolsExecutables[$toolName]
+                $foundVersion = Get-Item $expectedVersionPath `
+                    | Sort-Object -Property {[version]$_.name} -Descending `
+                    | Select-Object -First 1
+                $foundVersionPath = Join-Path $foundVersion $tool.arch
+
+                if($toolExecs) {
+                    foreach ($executable in $toolExecs["tools"]) {
+                        $executablePath = Join-Path $foundVersionPath $executable   
+    
+                        It "Validate $executable" -TestCases @{ExecutablePath = $executablePath} {
+                            $ExecutablePath | Should -Exist
+                        }
+                    }
+                }
+            }
+        }
+    }
+}