Warning message

Tasks/VsTest/Strings/resources.resjson/en-US/resources.resjson

@@ -107,5 +107,6 @@
   "loc.messages.testAssemblyFilterInput": "Test assembly filter : %s",
   "loc.messages.vsVersionSelected": "VisualStudio version selected for test execution : %s",
   "loc.messages.runTestsLocally": "Run the tests locally using %s....",
-  "loc.messages.vstestLocationSpecified": "%s, specified location : %s"
+  "loc.messages.vstestLocationSpecified": "%s, specified location : %s",
+  "loc.messages.uitestsparallel": "Running UI tests in parallel on the same machine can lead to errors. Consider disabling the ‘run in parallel’ option or run UI tests using a separate task. To learn more, see https://aka.ms/paralleltestexecution "
 }

Tasks/VsTest/task.json

@@ -395,7 +395,8 @@
         "testAssemblyFilterInput": "Test assembly filter : %s",
         "vsVersionSelected": "VisualStudio version selected for test execution : %s",
         "runTestsLocally": "Run the tests locally using %s....",
-        "vstestLocationSpecified": "%s, specified location : %s"
+        "vstestLocationSpecified": "%s, specified location : %s",
+        "uitestsparallel": "Running UI tests in parallel on the same machine can lead to errors. Consider disabling the ‘run in parallel’ option or run UI tests using a separate task. To learn more, see https://aka.ms/paralleltestexecution "
 
     }
 }

Tasks/VsTest/task.loc.json

@@ -395,6 +395,7 @@
     "testAssemblyFilterInput": "ms-resource:loc.messages.testAssemblyFilterInput",
     "vsVersionSelected": "ms-resource:loc.messages.vsVersionSelected",
     "runTestsLocally": "ms-resource:loc.messages.runTestsLocally",
-    "vstestLocationSpecified": "ms-resource:loc.messages.vstestLocationSpecified"
+    "vstestLocationSpecified": "ms-resource:loc.messages.vstestLocationSpecified",
+    "uitestsparallel": "ms-resource:loc.messages.uitestsparallel"
   }
 }

Tasks/VsTest/taskinputparser.ts

@@ -161,6 +161,11 @@ function initTestConfigurations(testConfiguration: models.TestConfigurations) {
         tl._writeLine(tl.loc('vstestLocationSpecified', 'vstest.console.exe', testConfiguration.vsTestLocation));
     }
 
+    if(tl.getBoolInput('uiTests') && testConfiguration.runInParallel)
+    {
+        tl.warning(tl.loc('uitestsparallel'));
+    }
+
         // only to facilitate the writing of unit tests 
     testConfiguration.vs15HelperPath = tl.getVariable('vs15Helper');
     if (!testConfiguration.vs15HelperPath) {

Tests-Legacy/L0/VsTest/_suite.ts

@@ -406,6 +406,33 @@ describe('VsTest Suite', function () {
             });
     })
 
+    it('Vstest task with run in parallel and UI tests', (done) => {
+
+        let vstestCmd = [sysVstestLocation, '/source/dir/someFile1', '/logger:trx'].join(' ');
+        setResponseFile('vstestGood.json');
+
+        let tr = new trm.TaskRunner('VSTest');
+        tr.setInput('testSelector', 'testAssemblies');        
+        tr.setInput('testAssemblyVer2', '/source/dir/someFile1');
+        tr.setInput('vstestLocationMethod', 'version');
+        tr.setInput('vsTestVersion', '14.0');
+        tr.setInput('uiTests', 'true');
+        tr.setInput('runInParallel', 'true');
+
+        tr.run()
+            .then(() => {
+                assert(tr.resultWasSet, 'task should have set a result');
+                assert(tr.stderr.length === 0, 'should not have written to stderr. error: ' + tr.stderr);
+                assert(tr.succeeded, 'task should have succeeded');
+                assert(tr.ran(vstestCmd), 'should have run vstest');
+                assert(tr.stdout.search(/Running UI tests in parallel on the same machine can lead to errors. Consider disabling the ‘run in parallel’ option or run UI tests using a separate task./) >= 0, 'should have given a warning for ui tests and run in parallel selection.');
+                done();
+            })
+            .fail((err) => {
+                done(err);
+            });
+    })
+
     it('Vstest task with run in parallel and vs 2013', (done) => {
 
         let vstestCmd = [sysVstestLocation, '/source/dir/someFile1', '/logger:trx'].join(' ');