Add a ICodeLensProvider for running Pester tests

This change adds an ICodeLensProvider implementation which adds
CodeLenses on Pester "Describe" blocks so that the tests in these blocks
can be ran or debugged easily from within an editor.

Author: daviwil

src/PowerShellEditorServices.Host/CodeLens/CodeLensFeature.cs

@@ -58,6 +58,9 @@ public static CodeLensFeature Create(
                 new ReferencesCodeLensProvider(
                     editorSession));
 
+            codeLenses.Providers.Add(
+                new PesterCodeLensProvider(
+                    editorSession));
 
             editorSession.Components.Register<ICodeLenses>(codeLenses);
 

src/PowerShellEditorServices.Host/CodeLens/PesterCodeLensProvider.cs

@@ -0,0 +1,99 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Microsoft.PowerShell.EditorServices.Commands;
+using Microsoft.PowerShell.EditorServices.Symbols;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Microsoft.PowerShell.EditorServices.CodeLenses
+{
+    internal class PesterCodeLensProvider : FeatureProviderBase, ICodeLensProvider
+    {
+        private static char[] QuoteChars = new char[] { '\'', '"'};
+
+        private EditorSession editorSession;
+        private IDocumentSymbolProvider symbolProvider;
+
+        public PesterCodeLensProvider(EditorSession editorSession)
+        {
+            this.editorSession = editorSession;
+            this.symbolProvider = new PesterDocumentSymbolProvider();
+        }
+
+        private IEnumerable<CodeLens> GetPesterLens(
+            SymbolReference symbol,
+            ScriptFile scriptFile)
+        {
+            // Trim the Describe "" { from the symbol name
+            int startQuoteIndex = symbol.SourceLine.IndexOfAny(QuoteChars) + 1;
+            int endQuoteIndex =  symbol.SourceLine.LastIndexOfAny(QuoteChars);
+
+            string describeBlockName =
+                symbol.SourceLine.Substring(
+                    startQuoteIndex,
+                    endQuoteIndex - startQuoteIndex);
+
+            var clientCommands = new ClientCommand[]
+            {
+                new ClientCommand(
+                    "PowerShell.RunPesterTests",
+                    "run tests",
+                    new object[]
+                    {
+                        scriptFile.ClientFilePath,
+                        false, // Don't debug
+                        describeBlockName,
+                    }),
+
+                new ClientCommand(
+                    "PowerShell.RunPesterTests",
+                    "debug tests",
+                    new object[]
+                    {
+                        scriptFile.ClientFilePath,
+                        true, // Run in debugger
+                        describeBlockName,
+                    }),
+            };
+
+            return
+                clientCommands.Select(
+                    command =>
+                        new CodeLens(
+                            this,
+                            scriptFile,
+                            symbol.ScriptRegion,
+                            command));
+        }
+
+        public CodeLens[] ProvideCodeLenses(ScriptFile scriptFile)
+        {
+            var symbols =
+                this.symbolProvider
+                    .ProvideDocumentSymbols(scriptFile);
+
+            var lenses =
+                symbols
+                    .Where(s => s.SymbolName.StartsWith("Describe"))
+                    .SelectMany(s => this.GetPesterLens(s, scriptFile))
+                    .ToArray();
+
+            return lenses;
+        }
+
+        public Task<CodeLens> ResolveCodeLensAsync(
+            CodeLens codeLens,
+            CancellationToken cancellationToken)
+        {
+            // This provider has no specific behavior for
+            // resolving CodeLenses.
+            return Task.FromResult(codeLens);
+        }
+    }
+}