`NullReferenceException` when running multiple tests

[benm-eras]

Firstly, thank you for this awesome library, without it I wouldn't be able to use Blazor!

I am getting a NullReferenceException on start up when running more than one unit test using Microsoft.VisualStudio.TestTools.UnitTesting.WebApplicationFactory . I have created a minimal reproduction (just the Blazor Server template with Blazor.Polyfill and a test project added) of the issue here, just run all the tests (there are only 2) at once and you should get the following exception:

System.NullReferenceException: Object reference not set to an instance of an object. at React.AspNet.HttpContextLifetimeProvider.get_Registrations() at React.AspNet.HttpContextLifetimeProvider.ReleaseObject() at React.TinyIoC.TinyIoCContainer.CustomObjectLifetimeFactory.Dispose() at React.TinyIoC.SafeDictionary2.set_Item(TKey key, TValue value) at React.TinyIoC.TinyIoCContainer.AddUpdateRegistration(TypeRegistration typeRegistration, ObjectFactoryBase factory) at React.TinyIoC.TinyIoCContainer.RegisterInternal(Type registerType, String name, ObjectFactoryBase factory) at React.TinyIoC.TinyIoCContainer.Register(Type registerType, Type registerImplementation) at React.TinyIoC.TinyIoCContainer.Register[RegisterType,RegisterImplementation]() at React.AssemblyRegistration.Register(TinyIoCContainer container) at React.Initializer.InitializeIoC(Func2 requestLifetimeRegistration) at React.Initializer.Initialize(Func2 requestLifetimeRegistration) at React.AspNet.ReactBuilderExtensions.UseReact(IApplicationBuilder app, Action1 configure, BabelFileOptions fileOptions) at Blazor.Polyfill.Server.BlazorPolyfillMiddlewareExtensions.InitReact(IApplicationBuilder builder) at Blazor.Polyfill.Server.BlazorPolyfillMiddlewareExtensions.UseBlazorPolyfill(IApplicationBuilder builder, BlazorPolyfillOptions options) at Blazor.Polyfill.Server.BlazorPolyfillMiddlewareExtensions.UseBlazorPolyfill(IApplicationBuilder builder, Action`1 configureOptions) at Blazor.Polyfill.Server.BlazorPolyfillMiddlewareExtensions.UseBlazorPolyfill(IApplicationBuilder builder) at Blazor.Polyfill.Startup.Configure(IApplicationBuilder app, IWebHostEnvironment env) in C:\Users\BenMiller\Downloads\Blazor.Polyfill\Blazor.Polyfill\Startup.cs:line 51 at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor, Boolean wrapExceptions) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at Microsoft.AspNetCore.Hosting.ConfigureBuilder.Invoke(Object instance, IApplicationBuilder builder) at Microsoft.AspNetCore.Hosting.ConfigureBuilder.<>cDisplayClass4_0.b0(IApplicationBuilder builder) at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<>cDisplayClass15_0.b1(IApplicationBuilder app) at Microsoft.AspNetCore.Mvc.Filters.MiddlewareFilterBuilderStartupFilter.<>cDisplayClass0_0.gMiddlewareFilterBuilder|0(IApplicationBuilder builder) at Microsoft.AspNetCore.HostFilteringStartupFilter.<>cDisplayClass0_0.b0(IApplicationBuilder app) at Microsoft.AspNetCore.Hosting.GenericWebHostService.StartAsync(CancellationToken cancellationToken)

Rather confusingly I named my project Blazor.Polyfill so it's not abundantly clear in the stack trace above, but my call to add your middleware with Blazor.Polyfill.Server.BlazorPolyfillMiddlewareExtensions.UseBlazorPolyfill(IApplicationBuilder builder) is the (slightly) bold line above.

My tests all pass when I run them one at a time, and I have turned off the option to run tests in parallel, but if I try running more than one test at a time I get the exception above.

Do you have any ideas?

UPDATE:

I have fixed an issue with my reproduction project, I messed up when adding to source control and excluded the test project

[Daddoon]

Well, i think the issue is:

• I don't do any extended check if the initialization is called twice
• Also i don't think there is any way to unload / reset the Javascript Engine logic used by React.NET library that is used at BlazorPolyfill boot. This library is needed for Javascript transpilation on the fly, as Babel is embedded in it.

See source code here: https://github.com/Daddoon/Blazor.Polyfill/blob/13c1c251f9488aea87ab2b912421a63297598141/src/Blazor.Polyfill.Server/BlazorPolyfillMiddlewareExtensions.cs

I'm not a Unit testing expert. So i would like to know, is yours tests all launched in the same AppDomain / Memory at unit testing ?

I think the error would probably disappear if each tests is loaded in a different AppDomain, as React would not be statically registered twice i imagine, same for low-level Javascript Engine library, at least not in the shared memory.

Keep me informed !