relative path for test dlls as arguments

src/Microsoft.TestPlatform.CoreUtilities/Helpers/FileHelper.cs

@@ -52,5 +52,17 @@ public FileAttributes GetFileAttributes(string path)
         {
             return new FileInfo(path).Attributes;
         }
+
+        /// <inheritdoc/>
+        public bool IsRootedPath(string path)
+        {
+            return Path.IsPathRooted(path);
+        }
+
+        /// <inheritdoc/>
+        public string CombinePath(string source)
+        {
+            return Path.Combine(Directory.GetCurrentDirectory(), source);
+        }
     }
 }

src/Microsoft.TestPlatform.CoreUtilities/Helpers/Interfaces/IFileHelper.cs

@@ -56,5 +56,19 @@ public interface IFileHelper
         /// <param name="path">Full path of the file.</param>
         /// <returns>Attributes of the file.</returns>
         FileAttributes GetFileAttributes(string path);
+
+        /// <summary>
+        /// Check if file path is rooted.
+        /// </summary>
+        /// <param name="path">Full path of the file.</param>
+        /// <returns>Is file path rooted.</returns>
+        bool IsRootedPath(string path);
+
+        /// <summary>
+        /// Create full file path.
+        /// </summary>
+        /// <param name="path">relative path of the file.</param>
+        /// <returns>Full file path, based on current working directory.</returns>
+        string CombinePath(string source);
     }
 }

src/vstest.console/CommandLine/CommandLineOptions.cs

@@ -253,6 +253,12 @@ public void AddSource(string source)
             }
 
             source = source.Trim();
+
+            if(!FileHelper.IsRootedPath(source))
+            {
+                source = FileHelper.CombinePath(source);
+            }
+
             if (!FileHelper.Exists(source))
             {
                 throw new CommandLineException(