For months now, the music industry has been conducting a test. The latest guinea pig is Gwen Stefani, and she has passed with flying colors.

The test boils down to a simple question: If an album is not on Spotify, can it still go to No. 1? Taylor Swift and Adele both showed it was possible, but their albums were exceptional blockbusters. And while the big record labels are not crazy about the fact that Spotify makes music available free, that streaming service’s powerful size — it has 30 million paying customers around the world, and tens of millions more who listen free — makes it hard to ignore.

Yet Ms. Stefani’s latest album, “This Is What the Truth Feels Like” (Interscope), is the latest big release to be “windowed” — available at some online outlets but not others — and still go to No. 1, Ms. Stefani’s first time at the spot as a solo act. The album, which is on Apple, Tidal and Amazon, and also got a promotional push from Target, sold 76,000 copies in its first week out in the United States and had a modest 3.8 million streams, according to Nielsen. While several singles from the album are on Spotify, the service is not scheduled to get the whole LP until Friday.

So is the test complete? Probably not, since the results so far are inconclusive. This month the British band the 1975 also went to No. 1 with its latest album despite its initial absence from Spotify. But when Coldplay took a similar route, it stalled at No. 2. Next week’s top album is likely to be the first solo release from Zayn of One Direction, whose popularity on Spotify has made him the service’s ninth most popular act. (The No. 1 artist on Spotify, by the way, is Justin Bieber, who has likewise embraced the platform.)