Fixing merge conflicts.

src/Adapter/MSTestAdapter/Execution/TestExecutionManager.cs

@@ -102,8 +102,11 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution
                 var logger = (IMessageLogger)frameworkHandle;
                 
                 // discover the tests
-                (new UnitTestDiscoverer()).DiscoverTestsInSource(source, logger, discoverySink, runContext?.RunSettings);
+                this.GetUnitTestDiscoverer().DiscoverTestsInSource(source, logger, discoverySink, runContext?.RunSettings);
                 tests.AddRange(discoverySink.Tests);
+
+                //Clear discoverSinksTests so that it just stores test for one source at one point of time
+                discoverySink.Tests.Clear();
             }
 
             bool isDeploymentDone = PlatformServiceProvider.Instance.TestDeployment.Deploy(tests, runContext, frameworkHandle);
@@ -123,7 +126,7 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution
         /// <summary>
         /// Execute the parameter tests
         /// </summary>
-        private void ExecuteTests(IEnumerable<TestCase> tests, IRunContext runContext, IFrameworkHandle frameworkHandle, bool isDeploymentDone)
+        internal virtual void ExecuteTests(IEnumerable<TestCase> tests, IRunContext runContext, IFrameworkHandle frameworkHandle, bool isDeploymentDone)
         {
             var testsBySource = (from test in tests
                                  group test by test.Source into testGroup
@@ -277,6 +280,11 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution
             this.LogWarnings(testExecutionRecorder, warnings);
         }
 
+        internal virtual UnitTestDiscoverer GetUnitTestDiscoverer()
+        {
+            return new UnitTestDiscoverer();
+        } 
+
         private void CacheSessionParameters(IRunContext runContext, ITestExecutionRecorder testExecutionRecorder)
         {
             if (!string.IsNullOrEmpty(runContext?.RunSettings?.SettingsXml))

src/Adapter/MSTestAdapter/MSTestDiscoverer.cs

@@ -117,7 +117,7 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter
         /// <param name="logger"> The logger. </param>
         /// <param name="discoverySink"> The discovery Sink. </param>
         /// <param name="runSettings"> The run settings. </param>
-        internal void DiscoverTestsInSource(
+        internal virtual void DiscoverTestsInSource(
             string source,
             IMessageLogger logger,
             ITestCaseDiscoverySink discoverySink,

test/UnitTests/MSTestAdapter.Tests/Discovery/UnitTestDiscovererTests.cs

@@ -261,4 +261,18 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTestAdapter.UnitTests.Discovery
 
         public int MaxLineNumber { get; set; }
     }
+
+    internal class TestableUnitTestDiscoverer : UnitTestDiscoverer
+    {
+        internal override void DiscoverTestsInSource(string source,
+            IMessageLogger logger,
+            ITestCaseDiscoverySink discoverySink,
+            IRunSettings runSettings)
+        {
+            var testCase1 = new TestCase("A", new System.Uri("executor://testExecutor"), source);
+            var testCase2 = new TestCase("B", new System.Uri("executor://testExecutor"), source);
+            discoverySink.SendTestCase(testCase1);
+            discoverySink.SendTestCase(testCase2);
+        }
+    }
 }

test/UnitTests/MSTestAdapter.Tests/Execution/TestExecutionManagerTests.cs

@@ -23,6 +23,7 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTestAdapter.UnitTests.Execution
 
     using Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.Execution;
     using Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.ObjectModel;
+    using Microsoft.VisualStudio.TestPlatform.MSTestAdapter.UnitTests.Discovery;
     using Microsoft.VisualStudio.TestPlatform.MSTestAdapter.UnitTests.TestableImplementations;
     using Microsoft.VisualStudio.TestPlatform.ObjectModel;
     using Microsoft.VisualStudio.TestPlatform.ObjectModel.Adapter;
@@ -352,6 +353,22 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTestAdapter.UnitTests.Execution
             Assert.IsNotNull(DummyTestClass.TestContextProperties);
         }
 
+        [TestMethodV1]
+        public void RunTestsForMultipleSourcesShouldRunEachTestJustOnce()
+        {
+            int testsCount = 0;
+            var sources = new List<string> { Assembly.GetExecutingAssembly().Location, Assembly.GetExecutingAssembly().Location };
+            TestableTestExecutionManager testableTestExecutionmanager = new TestableTestExecutionManager();
+
+            testableTestExecutionmanager.ExecuteTestsWrapper = (tests, runContext, frameworkHandle, isDeploymentDone) =>
+            {
+                testsCount += tests.Count();
+            };
+
+            testableTestExecutionmanager.RunTests(sources, this.runContext, this.frameworkHandle, this.cancellationToken);
+            Assert.AreEqual(testsCount, 4);
+        }
+
         #endregion
 
         #region private methods
@@ -568,5 +585,24 @@ namespace Microsoft.VisualStudio.TestPlatform.MSTestAdapter.UnitTests.Execution
         }
     }
 
+    internal class TestableTestExecutionManager : TestExecutionManager
+    {
+         internal override void ExecuteTests(IEnumerable<TestCase> tests, IRunContext runContext,
+         IFrameworkHandle frameworkHandle, bool isDeploymentDone)
+         {
+            if (this.ExecuteTestsWrapper != null)
+            {
+                this.ExecuteTestsWrapper.Invoke(tests, runContext, frameworkHandle, isDeploymentDone);
+            }
+         }
+
+         internal override UnitTestDiscoverer GetUnitTestDiscoverer()
+         {
+             return new TestableUnitTestDiscoverer();
+         }
+
+         internal Action<IEnumerable<TestCase>, IRunContext, IFrameworkHandle, bool> ExecuteTestsWrapper;
+    }
+
     #endregion
 }