Specflow - TearDown failed for test fixture - System.ArgumentNullException : Value cannot be null. (Parameter 'key')

Question

I'm working with test automation using Specflow and Selenium but by the time I try to execute my test, I face these error messages:

• My question is not what is a NullReferenceException, but what (and where) is this Parameter 'key' pointed as the cause of the exception.

TearDown failed for test fixture MyProject.Features.MyFeature System.ArgumentNullException : Value cannot be null. (Parameter 'key') TearDown : System.NullReferenceException : Object reference not set to an instance of an object.

And:

Error Message: OneTimeSetUp: System.ArgumentNullException : Value cannot be null. (Parameter 'key')

This is my scenario:

Scenario: Accessing the screen for the first time
    Given I accessed the screen for the first time
    Then the result grid should only show the phrase "Lorem ipsum"

This is my StepDefinition.cs file:

    [Binding]
    public class StepDefinition
    {
        PageObject pageObject = new PageObject();

        [Given(@"I accessed the screen for the first time")]
        public void GivenIAccessedTheScreenForTheFirstTime()
        {
            pageObject.NavigateToScreen();
        }

        [Then(@"the result grid should only show the phrase (.*)")]
        public void ThenTheResultGridShouldOnlyShowThePhrase(string phrase)
        {
            Assert.True(pageObject.isPhraseDisplayed(phrase));
        }        
    }

This is my PageObject.cs file:

        public PageObject() : base(){ } //I use a BasePageObject.cs file also

        public void NavigateToScreen()
        {
            driver.Navigate().GoToUrl(_urlHere_);
        }
        public bool isPhraseDisplayed(string phrase)
        {
            wait.Until(u => u.FindElement(_byIdOfWebElementHere_).Displayed);

            IWebElement element = driver.FindElement(_byIdOfWebElementHere_);
            return element.Displayed;
        }

And this is the BasePageObject.cs file, which implements IDisposable interface:

        protected IWebDriver driver { get; set; }
        protected WebDriverWait wait { get; set; }

        public BasePageObject()
        {
            driver = new ChromeDriver();
        }

        [AfterScenario]
        public void Dispose()
        {
            driver.Close();
            driver.Quit();
            driver.Dispose();
        }
    }

Exception Stack trace:

Starting test execution, please wait...

A total of 1 test files matched the specified pattern.
TearDown failed for test fixture MyProject.Features.MyFeature
System.ArgumentNullException : Value cannot be null. (Parameter 'key')
TearDown : System.NullReferenceException : Object reference not set to an instance of an object.
   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
   at System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value)
   at TechTalk.SpecFlow.Bindings.Discovery.RuntimeBindingRegistryBuilder.FindAttributeConstructorArg(ParameterInfo parameterInfo, Dictionary`2 namedAttributeValues)
   at TechTalk.SpecFlow.Bindings.Discovery.RuntimeBindingRegistryBuilder.<>c__DisplayClass8_0.<CreateAttribute>b__7(ParameterInfo p)
   at System.Linq.Enumerable.SelectArrayIterator`2.ToArray()
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at TechTalk.SpecFlow.Bindings.Discovery.RuntimeBindingRegistryBuilder.CreateAttribute(Attribute attribute)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.ToArray()
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at TechTalk.SpecFlow.Bindings.Discovery.RuntimeBindingRegistryBuilder.GetAttributes(IEnumerable`1 customAttributes)
   at TechTalk.SpecFlow.Bindings.Discovery.RuntimeBindingRegistryBuilder.CreateBindingSourceMethod(MethodInfo methodDefinition)
   at TechTalk.SpecFlow.Bindings.Discovery.RuntimeBindingRegistryBuilder.BuildBindingsFromType(Type type)
   at TechTalk.SpecFlow.Bindings.Discovery.RuntimeBindingRegistryBuilder.BuildBindingsFromAssembly(Assembly assembly)
   at TechTalk.SpecFlow.TestRunnerManager.BuildBindingRegistry(IEnumerable`1 bindingAssemblies)
   at TechTalk.SpecFlow.TestRunnerManager.InitializeBindingRegistry(ITestRunner testRunner)
   at TechTalk.SpecFlow.TestRunnerManager.CreateTestRunner(Int32 threadId)
   at TechTalk.SpecFlow.TestRunnerManager.GetTestRunnerWithoutExceptionHandling(Int32 threadId)
   at TechTalk.SpecFlow.TestRunnerManager.GetTestRunner(Int32 threadId)
   at TechTalk.SpecFlow.TestRunnerManager.GetTestRunner(Assembly testAssembly, Nullable`1 managedThreadId)
   at MyProject.Features.MyFeature.FeatureSetup()
--TearDown
   at MyProject.Features.MyFeature.FeatureTearDown()
  X AcessandoATelaDeConsultaPelaPrimeiraVez [< 1ms]
  Error Message:
   OneTimeSetUp: System.ArgumentNullException : Value cannot be null. (Parameter 'key')

Results File: C:\Users\FAMG\AppData\Local\Temp\test-explorer-GvcYR7\0.trx

Total tests: 1
     Failed: 1
 Total time: 3,7733 Seconds

Things I think are important to point:

• I am using VSCode, not Visual Studio.
• The test runner I have installed on my project is NUnit.

Answer 1

I just ran to this exact thing.
The source of the error comes from the reflection on type: System.Runtime.CompilerServices.NullableContextAttribute.

Looks like some kind of expected constructor MethodInfo Name is NULL.

Long story short: .NET Core 2.1, 2.2 work. SpecFlow (3.0.225) doesn't seem to work with .Net Core 3.0.

Good News: Turn on include pre-release for Nuget and get the beta SpecFlow and associated packages (Nunit and friends) updating to (3.1.52-beta) the latest works.

SpecFlow 3.1 main release will probably support .Net Core 3.0.