ContosoUniversityDotNetCore-Pages SliceFixture with AutoMapper - unit-testing

Question

My Create handler uses AutoMapper to map from command to entity.
public async Task<int> Handle(Command command, CancellationToken cancellationToken)
{
var entity = _mapper.Map<ExampleEntity>(command);
await _db.ExampleEntity.AddAsync(entity, cancellationToken);
await _db.SaveChangesAsync(cancellationToken);
return entity.Id;
}
My test looks like this
var command = new Create.Command
{
Name = "Example 1",
...
};
var id = await _fixture.SendAsync(command, mapper);
id.ShouldNotBeNull();
This is the SliceFixture
[CollectionDefinition(nameof(SliceFixture))]
public class SliceFixtureCollection : ICollectionFixture<SliceFixture> { }
public class SliceFixture : IAsyncLifetime
{
private readonly Checkpoint _checkpoint;
private readonly IConfiguration _configuration;
private readonly IServiceScopeFactory _scopeFactory;
private readonly WebApplicationFactory<Startup> _factory;
public SliceFixture()
{
_factory = new ContosoTestApplicationFactory();
_configuration = _factory.Services.GetRequiredService<IConfiguration>();
_scopeFactory = _factory.Services.GetRequiredService<IServiceScopeFactory>();
_checkpoint = new Checkpoint();
}
public class ContosoTestApplicationFactory : WebApplicationFactory<Startup>
{
protected override void ConfigureWebHost(IWebHostBuilder builder)
{
builder.ConfigureAppConfiguration((_, configBuilder) =>
{
configBuilder.AddInMemoryCollection(new Dictionary<string, string>
{
{"ConnectionStrings:DefaultConnection", _connectionString}
});
});
}
private readonly string _connectionString = "";
}
public async Task ExecuteScopeAsync(Func<IServiceProvider, Task> action)
{
using var scope = _scopeFactory.CreateScope();
var dbContext = scope.ServiceProvider.GetRequiredService<SchoolContext>();
try
{
await dbContext.BeginTransactionAsync();
await action(scope.ServiceProvider);
await dbContext.CommitTransactionAsync();
}
catch (Exception)
{
dbContext.RollbackTransaction();
throw;
}
}
public async Task<T> ExecuteScopeAsync<T>(Func<IServiceProvider, Task<T>> action)
{
using var scope = _scopeFactory.CreateScope();
var dbContext = scope.ServiceProvider.GetRequiredService<SchoolContext>();
try
{
await dbContext.BeginTransactionAsync();
var result = await action(scope.ServiceProvider);
await dbContext.CommitTransactionAsync();
return result;
}
catch (Exception)
{
dbContext.RollbackTransaction();
throw;
}
}
public Task ExecuteDbContextAsync(Func<SchoolContext, Task> action) => ExecuteScopeAsync(sp => action(sp.GetService<SchoolContext>()));
public Task ExecuteDbContextAsync(Func<SchoolContext, ValueTask> action) => ExecuteScopeAsync(sp => action(sp.GetService<SchoolContext>()).AsTask());
public Task ExecuteDbContextAsync(Func<SchoolContext, IMediator, Task> action) => ExecuteScopeAsync(sp => action(sp.GetService<SchoolContext>(), sp.GetService<IMediator>()));
public Task<T> ExecuteDbContextAsync<T>(Func<SchoolContext, Task<T>> action) => ExecuteScopeAsync(sp => action(sp.GetService<SchoolContext>()));
public Task<T> ExecuteDbContextAsync<T>(Func<SchoolContext, ValueTask<T>> action) => ExecuteScopeAsync(sp => action(sp.GetService<SchoolContext>()).AsTask());
public Task<T> ExecuteDbContextAsync<T>(Func<SchoolContext, IMediator, Task<T>> action) => ExecuteScopeAsync(sp => action(sp.GetService<SchoolContext>(), sp.GetService<IMediator>()));
public Task InsertAsync<T>(params T[] entities) where T : class
{
return ExecuteDbContextAsync(db =>
{
foreach (var entity in entities)
{
db.Set<T>().Add(entity);
}
return db.SaveChangesAsync();
});
}
public Task<T> FindAsync<T>(int id)
where T : class, IEntity
{
return ExecuteDbContextAsync(db => db.Set<T>().FindAsync(id).AsTask());
}
public Task<TResponse> SendAsync<TResponse>(IRequest<TResponse> request)
{
return ExecuteScopeAsync(sp =>
{
var mediator = sp.GetRequiredService<IMediator>();
return mediator.Send(request);
});
}
public Task SendAsync(IRequest request)
{
return ExecuteScopeAsync(sp =>
{
var mediator = sp.GetRequiredService<IMediator>();
return mediator.Send(request);
});
}
private int _courseNumber = 1;
public int NextCourseNumber() => Interlocked.Increment(ref _courseNumber);
public Task InitializeAsync() => _checkpoint.Reset(_configuration.GetConnectionString("DefaultConnection"));
public Task DisposeAsync()
{
_factory?.Dispose();
return Task.CompletedTask;
}
}
When I run the test I get -
Object reference not set to an instance of an object.
because _mapper is null.
I know I probably need to modify the SliceFixture but can't figure out what to do.
I was looking to implement Jimmy’s example here with the additional AutoMapper implementation.