added test for the output with build server and json when running in …

…build server

src/GitVersionExe.Tests/ExecutionResults.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using Newtonsoft.Json;
 using GitVersion.OutputVariables;
@@ -21,7 +22,10 @@ public virtual VersionVariables OutputVariables
         {
             get
             {
-                var outputVariables = JsonConvert.DeserializeObject<Dictionary<string, string>>(Output);
+                var jsonStartIndex = Output.IndexOf("{", StringComparison.Ordinal);
+                var json = Output.Substring(jsonStartIndex);
+
+                var outputVariables = JsonConvert.DeserializeObject<Dictionary<string, string>>(json);
                 return VersionVariables.FromDictionary(outputVariables);
             }
         }

src/GitVersionExe.Tests/JsonOutputOnBuildServerTest.cs

@@ -0,0 +1,45 @@
+using System.Collections.Generic;
+using GitTools.Testing;
+using GitVersion.BuildServers;
+using NUnit.Framework;
+using Shouldly;
+
+namespace GitVersionExe.Tests
+{
+    public class JsonOutputOnBuildServerTest
+    {
+        [Test]
+        public void BeingOnBuildServerDoesntOverrideOutputJson()
+        {
+            using var fixture = new RemoteRepositoryFixture();
+            fixture.Repository.MakeATaggedCommit("1.2.3");
+            fixture.Repository.MakeACommit();
+
+            var env = new KeyValuePair<string, string>(TeamCity.EnvironmentVariableName, "8.0.0");
+
+            var result = GitVersionHelper.ExecuteIn(fixture.LocalRepositoryFixture.RepositoryPath, arguments: " /output json", environments: env);
+
+            result.ExitCode.ShouldBe(0);
+            result.Output.ShouldStartWith("{");
+            result.Output.TrimEnd().ShouldEndWith("}");
+        }
+
+        [Test]
+        public void BeingOnBuildServerWithOutputJsonDoesNotFail()
+        {
+            using var fixture = new RemoteRepositoryFixture();
+            fixture.Repository.MakeATaggedCommit("1.2.3");
+            fixture.Repository.MakeACommit();
+
+            var env = new KeyValuePair<string, string>(TeamCity.EnvironmentVariableName, "8.0.0");
+
+            var result = GitVersionHelper.ExecuteIn(fixture.LocalRepositoryFixture.RepositoryPath, arguments: " /output json /output buildserver", environments: env);
+
+            result.ExitCode.ShouldBe(0);
+            const string version = "0.1.0+4";
+            result.Output.ShouldContain($"##teamcity[buildNumber '{version}']");
+            result.OutputVariables.ShouldNotBeNull();
+            result.OutputVariables.FullSemVer.ShouldBeEquivalentTo(version);
+        }
+    }
+}

src/GitVersionExe/ArgumentParser.cs

@@ -279,7 +279,7 @@ public Arguments ParseArguments(string[] commandLineArguments)
                     {
                         if (!Enum.TryParse(v, true, out OutputType outputType))
                         {
-                            throw new WarningException($"Value '{value}' cannot be parsed as output type, please use 'json' or 'buildserver'");
+                            throw new WarningException($"Value '{v}' cannot be parsed as output type, please use 'json' or 'buildserver'");
                         }
 
                         arguments.Output.Add(outputType);