Lingering File Handles (#71)

Fixing a bug where in various situations, the files used for temporary storage of query results would be leftover. In particular, the following changes were made:
* When the dispose query request is submitted, the corresponding query is now disposed in addition from being removed from the list of active queries
* When a query is cancelled, it is disposed after it is cancelled
* If a query already exists for a given ownerURI, the existing query is disposed before creating a new query
* All queries are disposed when the query execution service is disposed (ie, at shutdown of the service)

A unit test to verify the action of the dispose method for a ResultSet was added.

* Ensuring queries are disposed

Adding logic to dispose any queries when:
* URI that already has a query executes another query
* A request to dispose a query is submitted
* A request to cancel a query is submitted

* Small tweaks for cleanup of query execution service

test/Microsoft.SqlTools.ServiceLayer.Test/QueryExecution/DisposeTests.cs

@@ -4,9 +4,12 @@
 //
 
 using System;
+using System.Data.Common;
 using System.Threading.Tasks;
 using Microsoft.SqlTools.ServiceLayer.Hosting.Protocol;
+using Microsoft.SqlTools.ServiceLayer.QueryExecution;
 using Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts;
+using Microsoft.SqlTools.ServiceLayer.QueryExecution.DataStorage;
 using Microsoft.SqlTools.ServiceLayer.SqlContext;
 using Microsoft.SqlTools.ServiceLayer.Test.Utility;
 using Microsoft.SqlTools.ServiceLayer.Workspace;
@@ -18,6 +21,21 @@ namespace Microsoft.SqlTools.ServiceLayer.Test.QueryExecution
 {
     public class DisposeTests
     {
+        [Fact]
+        public void DisposeResultSet()
+        {
+            // Setup: Mock file stream factory, mock db reader
+            var mockFileStreamFactory = new Mock<IFileStreamFactory>();
+            var mockDataReader = Common.CreateTestConnection(null, false).CreateCommand().ExecuteReaderAsync().Result;
+            
+            // If: I setup a single resultset and then dispose it
+            ResultSet rs = new ResultSet(mockDataReader, mockFileStreamFactory.Object);
+            rs.Dispose();
+
+            // Then: The file that was created should have been deleted
+            mockFileStreamFactory.Verify(fsf => fsf.DisposeFile(It.IsAny<string>()), Times.Once);
+        }
+
         [Fact]
         public void DisposeExecutedQuery()
         {
@@ -70,6 +88,37 @@ namespace Microsoft.SqlTools.ServiceLayer.Test.QueryExecution
             Assert.NotEmpty(result.Messages);
         }
 
+        [Fact]
+        public async Task ServiceDispose()
+        {
+            // Setup:
+            // ... We need a workspace service that returns a file
+            var fileMock = new Mock<ScriptFile>();
+            fileMock.SetupGet(file => file.Contents).Returns(Common.StandardQuery);
+            var workspaceService = new Mock<WorkspaceService<SqlToolsSettings>>();
+            workspaceService.Setup(service => service.Workspace.GetFile(It.IsAny<string>()))
+                .Returns(fileMock.Object);
+            // ... We need a query service
+            var queryService = Common.GetPrimedExecutionService(Common.CreateMockFactory(null, false), true,
+                workspaceService.Object);
+
+            // If:
+            // ... I execute some bogus query
+            var queryParams = new QueryExecuteParams { QuerySelection = Common.WholeDocument, OwnerUri = Common.OwnerUri };
+            var requestContext = RequestContextMocks.Create<QueryExecuteResult>(null);
+            await queryService.HandleExecuteRequest(queryParams, requestContext.Object);
+
+            // ... And it sticks around as an active query
+            Assert.Equal(1, queryService.ActiveQueries.Count);
+
+            // ... The query execution service is disposed, like when the service is shutdown
+            queryService.Dispose();
+
+            // Then:
+            // ... There should no longer be an active query
+            Assert.Empty(queryService.ActiveQueries);
+        }
+
         #region Mocking
 
         private Mock<RequestContext<QueryDisposeResult>> GetQueryDisposeResultContextMock(