How do I unit test implementations of IEntityTypeConfiguration

I hope this is the right place to ask this question. I am working on a class that extends IEntityTypeConfiguration and I want to unit test code that usually runs in DbContext.OnModelCreating.

For example:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
  modelBuilder.ApplyConfiguration(new MyCustomConfig("./some-seed-data.json"));
  modelBuilder.ApplyConfiguration(new MyOtherCustomConfig());
}

Should I be instantiating a ModelBuilder? I would prefer to not run a migration that creates files but that’s an acceptable side-effect.

Thanks

EF Core version: <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.1.0" /> Database Provider: <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.1.0" /> Operating system: Win 10 IDE: (e.g. Visual Studio 2017 15.4) VS Code

[gforceg]

@ajcvickers, I am working on an abstract class that makes method calls in Configure() to perform configuration and to seed data from the file system (json, yaml, etc…).

public abstract class EntityConfiguration<TEntity> : IEntityTypeConfiguration<TEntity>
  where TEntity : class
  {
    public string FilePath { get; set; }
    
    public EntityConfiguration(string filePath = "")
    {
      this.FilePath = filePath;
    }

    public void Configure(EntityTypeBuilder<TEntity> builder)
    {
      DoConfiguration(builder);
      DoSeed(builder);
    }
    ...
}

I think what I’m currently trying to do is an integration test. I have a class ‘MyCustomConfig’ that inherits from EntityConfiguration. I want to assert that the following code will throw an exception when the json file doesn’t exist.

modelBuilder.ApplyConfiguration(new MyCustomConfig("./non-existent-file.json"));

I must wrap the call in modelBuilder.ApplyConfiguration otherwise, MyCustomConfig.Configure won’t be called. The only way I know how to do this is by running a migration from the dotnet cli and I think that would be more of a BDD test.

I would also like to be able to unit test the individual DoConfiguration(builder) and DoSeed(builder) functions but I don’t know how to instantiate EntityTypeBuilder.

[norcino]

You can unit test how your configuration is altering the builder using the following:

    var sut = new ScoringAssessmentOutcomeEntityTypeConfiguration();
    var entityType = new EntityType("MyType", typeof(MyType), new Model(), false, ConfigurationSource.Convention);            
     var builder = new EntityTypeBuilder<MyType>(entityType);
     
     sut.Configure(builder);

     var meta = builder.Metadata;
     var properties = builder.Metadata.GetDeclaredProperties();
     var viewName = builder.Metadata.GetViewName();