property of UIContentConfiguration cannot be called

Looks as if content was optional ('UIContentConfiguration?'), which is surprising, but.

Could you test:

Code Block 
    let registration = UICollectionView.CellRegistration<UICollectionViewListCell, Article> { cell, _, item in
      if var content = cell.defaultContentConfiguration() {
        content.text = "title"
        cell.contentConfiguration = content
      }
    }

Something strange on this forum.

The abstract of your question is:
private func setupCollectionView() {    let registration = UICollectionView.CellRegistrationUICollectionViewListCell, Article { cell, _, item in      var content = cell.defaultContentConfiguration()      content.text = "title" 

And the first line

Code Block 
private func setupCollectionView() {

doesn't show in the post itself !

Now back to your question.

I tested your code (which is exactly what is proposed in documentation), and initially I got content type as UIContentConfiguration (which is a protocol) not UIListContentConfiguration (which is a struct with text property).

Could you check the type of content ? Error message seems to show it is UIContentConfiguration

So you could also test

Code Block 
   let registration = UICollectionView.CellRegistration<UICollectionViewListCell, Article> { cell, _, item in
      if var content = cell.defaultContentConfiguration() as? UIListContentConfiguration  {
        content.text = "title"
        cell.contentConfiguration = content
      }
    }

Note: I tested the following

Code Block 
 let registration = UICollectionView.CellRegistration<UICollectionViewListCell, Int> { cell, _, item in
       var content = cell.defaultContentConfiguration() as? UIContentConfiguration
       content.text = "title"
       cell.contentConfiguration = content
}

and got the exact same error message as yours :

Value of type 'UIContentConfiguration?' has no member 'text'.

That seems to confirm the problem.

Thank you for your answers!
I missed the difference UIContentConfiguration and UIListContentConfiguration.
I solved by rewriting as follows

Code Block 
    guard let content = cell.contentConfiguration as? UIListContentConfiguration else {
      XCTFail()
      return
    }
    XCTAssertEqual(content.text, "title")