it.skip("have all non-Widget view models from Python in the Models object", () => {
   const missing = []
   for (const name of core_defaults.all_view_model_names()) {
     if (!(name in Models.registered_names())) {
       missing.push(name)
     }
   }
   for (const m of missing) {
     console.log(`'Models.${m}' not found but there's a Python model '${m}'`)
   }
   expect(missing.length).to.equal(0)
 })

 it("have all view models from Python in registered locations", () => {
   const registered: {[key: string]: boolean} = {}
   for (const name of Models.registered_names()) {
     registered[name] = true
   }
   const missing = []
   const all_view_model_names = concat([core_defaults.all_view_model_names(), widget_defaults.all_view_model_names()])
   for (const name of all_view_model_names) {
     if (!(name in registered)) {
       missing.push(name)
     }
   }
   for (const m of missing) {
     console.log(`'base.locations["${m}"]' not found but there's a Python model '${m}'`)
   }
   expect(missing.length).to.equal(0)
 })

  constructor(attrs?: Partial<AnotherModel.Attrs>) {
    super(attrs)
  }

  static initClass(): void {
    this.prototype.type = 'AnotherModel'

    this.define<AnotherModel.Props>({
      bar: [ p.Number, 1 ],
    })
  }
}
AnotherModel.initClass()

Models.register('AnotherModel', AnotherModel)

namespace SomeModel {
  export type Attrs = p.AttrsOf<Props>
  export type Props = Model.Props & {
    foo: p.Property<number>
    child: p.Property<Model | null>
  }
}

interface SomeModel extends SomeModel.Attrs {}

class SomeModel extends Model {
  properties: SomeModel.Props

  constructor(attrs?: Partial<SomeModel.Attrs>) {