split parser definitions across multiple files

test/dotnet.Tests/ParserTests/AddReferenceParserTests.cs

@@ -0,0 +1,57 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.IO;
+using System.Linq;
+using FluentAssertions;
+using Microsoft.DotNet.Cli.CommandLine;
+using Microsoft.DotNet.Tools.Common;
+using Xunit;
+using Xunit.Abstractions;
+using Parser = Microsoft.DotNet.Cli.Parser;
+
+namespace Microsoft.DotNet.Tests.ParserTests
+{
+    public class AddReferenceParserTests
+    {
+        private readonly ITestOutputHelper output;
+
+        public AddReferenceParserTests(ITestOutputHelper output)
+        {
+            this.output = output;
+        }
+
+        [Fact]
+        public void AddReferenceHasDefaultArgumentSetToCurrentDirectory()
+        {
+            var command = Parser.DotnetCommand;
+
+            var result = command.Parse("dotnet add reference my.csproj");
+
+            output.WriteLine(result.Diagram());
+
+            result["dotnet"]["add"]
+                .Arguments
+                .Should()
+                .BeEquivalentTo(
+                    PathUtility.EnsureTrailingSlash(Directory.GetCurrentDirectory()));
+        }
+
+        [Fact]
+        public void AddReferenceWithoutArgumentResultsInAnError()
+        {
+            var command = Parser.DotnetCommand;
+
+            var result = command.Parse("dotnet add reference");
+
+            output.WriteLine(result.Diagram());
+
+            result
+                .Errors
+                .Select(e => e.Message)
+                .Should()
+                .BeEquivalentTo("Required argument missing for command: reference");
+        }
+    }
+}