Add unit tests for ErrorReportingSubsystem, with scope changes

Author: JeanJoeris

src/System.CommandLine.Subsystems.Tests/ErrorReportingSubsystemTests.cs

@@ -0,0 +1,70 @@
+// 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.Reflection;
+using FluentAssertions;
+using Xunit;
+using System.CommandLine.Parsing;
+using static System.Runtime.InteropServices.JavaScript.JSType;
+
+namespace System.CommandLine.Subsystems.Tests
+{
+    public class ErrorReportingSubsystemTests
+    {
+        [Fact]
+        public void Report_when_single_error_writes_to_console_hack()
+        {
+            var error = new ParseError("a sweet error message");
+            var errors = new List<ParseError> { error };
+            var errorSubsystem = new ErrorReportingSubsystem();
+            var consoleHack = new ConsoleHack().RedirectToBuffer(true);
+
+            errorSubsystem.Report(consoleHack, errors);
+
+            consoleHack.GetBuffer().Trim().Should().Be(error.Message);
+        }
+
+        [Fact]
+        public void Report_when_multiple_error_writes_to_console_hack()
+        {
+            var error = new ParseError("a sweet error message");
+            var anotherError = new ParseError("another sweet error message");
+            var errors = new List<ParseError> { error, anotherError };
+            var errorSubsystem = new ErrorReportingSubsystem();
+            var consoleHack = new ConsoleHack().RedirectToBuffer(true);
+
+            errorSubsystem.Report(consoleHack, errors);
+
+            consoleHack.GetBuffer().Trim().Should().Be($"{error.Message}\r\n{anotherError.Message}");
+        }
+
+        [Fact]
+        public void Report_when_no_errors_writes_nothing_to_console_hack()
+        {
+            var errors = new List<ParseError> { };
+            var errorSubsystem = new ErrorReportingSubsystem();
+            var consoleHack = new ConsoleHack().RedirectToBuffer(true);
+
+            errorSubsystem.Report(consoleHack, errors);
+
+            consoleHack.GetBuffer().Trim().Should().Be("");
+        }
+
+        [Theory]
+        [InlineData("-v", false)]
+        [InlineData("-x", true)]
+        [InlineData("", false)]
+        public void GetIsActivated_tests(string input, bool result)
+        {
+            var rootCommand = new CliRootCommand {new CliOption<bool>("-v")};
+            var configuration = new CliConfiguration(rootCommand);
+            var errorSubsystem = new ErrorReportingSubsystem();
+            Subsystem.Initialize(errorSubsystem, configuration);
+
+            var parseResult = CliParser.Parse(rootCommand, input, configuration);
+            var isActive = Subsystem.GetIsActivated(errorSubsystem, parseResult);
+
+            isActive.Should().Be(result);
+        }
+    }
+}

src/System.CommandLine.Subsystems.Tests/System.CommandLine.Subsystems.Tests.csproj

@@ -39,6 +39,7 @@
     <Compile Include="TestData.cs" />
     <Compile Include="VersionFunctionalTests.cs" />
     <Compile Include="VersionSubsystemTests.cs" />
+    <Compile Include="ErrorReportingSubsystemTests.cs" />
   </ItemGroup>
 
   <ItemGroup>

src/System.CommandLine/Parsing/ParseError.cs

@@ -10,7 +10,7 @@ public sealed class ParseError
     {
         // TODO: add position
         // TODO: reevaluate whether we should be exposing a SymbolResult here
-        internal ParseError(
+        public ParseError(
             string message, 
             SymbolResult? symbolResult = null)
         {