The instance of entity type cannot be tracked because another instance with the same key value for {'Id'} is already being tracked

I am aware that such question has already been asked numerous times, but solutions did not help me. I try to unit test my code in XUnit, but have numerous issues with EF Core, here is one of them.

// db init
public static StoreContext ConfigureStoreContext(IServiceCollection services, ITestOutputHelper output)
{
        services.AddDbContext<StoreContext>(c =>
            c.UseInMemoryDatabase(Guid.NewGuid().ToString()));

        var serviceProvider = services.BuildServiceProvider();
        var context = serviceProvider.GetRequiredService<StoreContext>();
        StoreContextSeed.SeedStoreAsync(context);
        return context;
}

[Fact]
public async Task UpdateAsync()
{
    string newTitle = "newTitle1";
    int newBrandId = 3;
    //var item = await storeContext.Items.AsNoTracking().FirstOrDefaultAsync(); // result is the same
    var item = new Item()
    {
        Id = 1,
        BrandId = newBrandId,
        CategoryId = 1,
        MeasurementUnitId = 1,
        StoreId = 1,
        Title = newTitle
    };
    storeContext.Entry(item).State = EntityState.Detached; // has no effect, could be removed. 
    //if assign Deleted, then get error "can not update deleted item"
    await service.UpdateAsync(item); // exception inside
    var updatedItem = await storeContext.Items.AsNoTracking().FirstOrDefaultAsync();
    Assert.Equal(newTitle, updatedItem.Title);
    Assert.Equal(newBrandId, updatedItem.BrandId);
}

public async Task UpdateAsync(T entity)
{
    _dbContext.Entry(entity).State = EntityState.Modified; // exception when trying to change the state
    await _dbContext.SaveChangesAsync();
}

Further technical details

EF Core version: 2.1 Database Provider: InMemory Operating system: IDE: (Visual Studio 2017 15.7)

Test Name:	UnitTests.Services.StoreServiceTests.UpdateAsync
Test FullName:	UnitTests.Services.StoreServiceTests.UpdateAsync
Test Source:	C:\Users\kozachenkoav\source\repos\OctopusStore\UnitTests\Services\StoreServiceTests.cs : line 56
Test Outcome:	Failed
Test Duration:	0:00:02,242

Result StackTrace:	
at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.ThrowIdentityConflict(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(TKey key, InternalEntityEntry entry, Boolean updateDuplicate)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.StartTracking(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges)
   at Microsoft.EntityFrameworkCore.ChangeTracking.EntityEntry.set_State(EntityState value)
   at Infrastructure.Data.EfRepository`1.UpdateAsync(T entity) in C:\Users\kozachenkoav\source\repos\OctopusStore\Infrastructure\Data\EfRepository.cs:line 54
   at Infrastructure.Services.StoreService.UpdateAsync(Store store) in C:\Users\kozachenkoav\source\repos\OctopusStore\Infrastructure\Services\StoreService.cs:line 29
   at UnitTests.Services.StoreServiceTests.UpdateAsync() in C:\Users\kozachenkoav\source\repos\OctopusStore\UnitTests\Services\StoreServiceTests.cs:line 71
--- End of stack trace from previous location where exception was thrown ---
Result Message:	System.InvalidOperationException : The instance of entity type 'Store' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values