diff --git a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/AssemblyDefinitionInfo.cs b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/AssemblyDefinitionInfo.cs
index 1b831a4..529165c 100644
--- a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/AssemblyDefinitionInfo.cs
+++ b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/AssemblyDefinitionInfo.cs
@@ -70,6 +70,7 @@ public static AssemblyDefinitionInfo Parse(FileInfo file, UnityProjectInfo unity
             toReturn.BuiltInPackage = isBuiltInPackage;
             toReturn.Validate(unityProjectInfo.AvailablePlatforms);
             toReturn.PrecompiledAssemblyReferences = new HashSet<string>(toReturn.precompiledReferences?.Select(t => t.Replace(".dll", string.Empty)) ?? Array.Empty<string>());
+            toReturn.DefineConstraints = new HashSet<string>(toReturn.defineConstraints ?? (toReturn.defineConstraints = new string[0]));
             return toReturn;
         }
 
@@ -90,7 +91,9 @@ public static AssemblyDefinitionInfo Parse(FileInfo file, UnityProjectInfo unity
         [SerializeField]
         private string[] precompiledReferences = null;
         public bool autoReferenced;
-        public string[] defineConstraints;
+
+        [SerializeField]
+        private string[] defineConstraints = null;
 
         /// <summary>
         /// Gets or sets the parsed Guid of the AssemblyDefinition asset.
@@ -147,8 +150,16 @@ public static AssemblyDefinitionInfo Parse(FileInfo file, UnityProjectInfo unity
         /// </summary>
         public HashSet<string> PrecompiledAssemblyReferences { get; private set; }
 
+        /// <summary>
+        /// Gets assembly defintions that are nested (in terms of folder hierarchy) in respect to this assembly defintion.
+        /// </summary>
         public HashSet<AssemblyDefinitionInfo> NestedAssemblyDefinitionFiles { get; } = new HashSet<AssemblyDefinitionInfo>();
 
+        /// <summary>
+        /// Gets the define constraints for this assembly defintion.
+        /// </summary>
+        public HashSet<string> DefineConstraints { get; private set; }
+
         /// <summary>
         /// After it's parsed from JSON, this method should be invoked to validate some of the values and set additional properties.
         /// </summary>
diff --git a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/CSProjectInfo.cs b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/CSProjectInfo.cs
index b7c4689..2fa267d 100644
--- a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/CSProjectInfo.cs
+++ b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/CSProjectInfo.cs
@@ -5,7 +5,6 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
-using System.IO;
 using System.Linq;
 using UnityEditor;
 using UnityEngine;
@@ -138,12 +137,29 @@ private ReadOnlyDictionary<BuildTarget, CompilationPlatformInfo> GetCompilationP
             }
 
             // We only are an asmdef at this point, as above we handle all PredfinedAssemblies, then EditorAsmDef and PredefinedEditorAssembly for inEditor and not inEditor cases above
-            Func<CompilationPlatformInfo, bool> predicate = AssemblyDefinitionInfo.includePlatforms.Length > 0
-                ? predicate = (t) => AssemblyDefinitionInfo.includePlatforms.Contains(t.Name)
-                : predicate = (t) => !AssemblyDefinitionInfo.excludePlatforms.Contains(t.Name);
+            bool IsPlatformSupported(CompilationPlatformInfo platform)
+            {
+                HashSet<string> additionalSet = inEditor ? platform.AdditionalInEditorDefines : platform.AdditionalPlayerDefines;
+
+                // Check for defines to ensure they are included in the platform (differentiate between editor/player)
+                foreach (string define in AssemblyDefinitionInfo.DefineConstraints)
+                {
+                    if (!platform.CommonPlatformDefines.Contains(define) && !additionalSet.Contains(define))
+                    {
+                        return false;
+                    }
+                }
+
+                if (AssemblyDefinitionInfo.includePlatforms.Length > 0)
+                {
+                    return AssemblyDefinitionInfo.includePlatforms.Contains(platform.Name);
+                }
+                // else
+                return !AssemblyDefinitionInfo.excludePlatforms.Contains(platform.Name);
+            }
 
             return new ReadOnlyDictionary<BuildTarget, CompilationPlatformInfo>(
-                UnityProjectInfo.AvailablePlatforms.Where(predicate)
+                UnityProjectInfo.AvailablePlatforms.Where(IsPlatformSupported)
                     .ToDictionary(t => t.BuildTarget, t => t));
         }
 
diff --git a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/Exporters/TemplatedProjectExporter.cs b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/Exporters/TemplatedProjectExporter.cs
index 21cbe21..a8e8a39 100644
--- a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/Exporters/TemplatedProjectExporter.cs
+++ b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/Exporters/TemplatedProjectExporter.cs
@@ -413,6 +413,9 @@ void ProcessDefaultMappings(ProjectConfigurationMapping mapping, Dictionary<stri
                 }
             }
 
+            List<string> availablePlatformNames = unityProjectInfo.AvailablePlatforms.Select(t => t.Name).ToList();
+            Dictionary<string, List<string>> defaultPlatformsMap = new Dictionary<string, List<string>> { { "InEditor", availablePlatformNames }, { "Player", availablePlatformNames } };
+
             // Iterate over every project
             foreach (CSProjectInfo project in orderedProjects)
             {
@@ -442,7 +445,7 @@ void ProcessProjectPlatforms(string configuration, IEnumerable<string> platforms
                 ProcessProjectPlatforms("Player", enabledPlayerPlatforms);
 
                 // Add all other known solution mappings, map to itself or allowed mappings
-                ProcessDefaultMappings(mapping, new Dictionary<string, List<string>> { { "InEditor", enabledInEditorPlatforms }, { "Player", enabledPlayerPlatforms } });
+                ProcessDefaultMappings(mapping, defaultPlatformsMap);
             }
 
             // Process the Dependencies Project now
diff --git a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/UnityProjectInfo.cs b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/UnityProjectInfo.cs
index bf5e9f9..534a7a5 100644
--- a/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/UnityProjectInfo.cs
+++ b/Source/MSBuildTools.Unity/Packages/com.microsoft.msbuildforunity/Editor/ProjectGenerator/Scripts/UnityProjectInfo.cs
@@ -34,6 +34,16 @@ public class UnityProjectInfo : IDisposable
             { "Unity.ugui", "UnityEngine.UI" }
         };
 
+        /// <summary>
+        /// Another patching technique to add defines to some assembly defintion files. TestRunner for example, is only referenced by projects with UNITY_INCLUDE_TESTS and references nunit that has UNITY_INCLUDE_TESTS;
+        /// However it doesn't have the define itself. This breaks Player build, and as it appears that Unity specially handles this case as well.
+        /// </summary>
+        private static readonly Dictionary<string, List<string>> ImpliedDefinesForAsmDefs = new Dictionary<string, List<string>>()
+        {
+            { "UnityEditor.TestRunner", new List<string>(){ "UNITY_INCLUDE_TESTS" } },
+            { "UnityEngine.TestRunner", new List<string>(){ "UNITY_INCLUDE_TESTS" } },
+        };
+
         /// <summary>
         /// Gets the name of this Unity Project.
         /// </summary>
@@ -222,7 +232,7 @@ private Dictionary<string, CSProjectInfo> CreateUnityProjects(MSBuildToolsConfig
             }
 
             // Now we have all of the assembly definiton files, let's run a quick validation. 
-            CorrectReferences(asmDefInfoMap);
+            ValidateAndPatchAssemblyDefinitions(asmDefInfoMap);
 
             int index = 0;
             ProcessSortedAsmDef(asmDefDirectoriesSorted.ToArray(), ref index, (uri) => true, (a) => { });
@@ -243,7 +253,7 @@ private Dictionary<string, CSProjectInfo> CreateUnityProjects(MSBuildToolsConfig
         /// <summary>
         /// This performs reference correction, for example this corrects "Unity.ugui" to be "UnityEngine.UI" (a known error of TextMeshPro). For correction map see <see cref="ProjectAliases"/>.
         /// </summary>
-        private void CorrectReferences(Dictionary<string, AssemblyDefinitionInfo> asmDefInfoMap)
+        private void ValidateAndPatchAssemblyDefinitions(Dictionary<string, AssemblyDefinitionInfo> asmDefInfoMap)
         {
             foreach (KeyValuePair<string, AssemblyDefinitionInfo> asmDefPair in asmDefInfoMap)
             {
@@ -259,6 +269,14 @@ private void CorrectReferences(Dictionary<string, AssemblyDefinitionInfo> asmDef
                         }
                     }
                 }
+
+                if (ImpliedDefinesForAsmDefs.TryGetValue(asmDefPair.Key, out List<string> defines))
+                {
+                    foreach (string define in defines)
+                    {
+                        asmDefPair.Value.DefineConstraints.Add(define);
+                    }
+                }
             }
         }