Where does React’s `scryRenderedDOMComponentsWithClass` method name come from?

Short answer

“Scry” in this context just means “find all”. See this comment on ReactTestUtils.scryRenderedComponentsWithClass. It’s a single word, not an abbreviation, and it’s pronounced like “cry” but with an “s” at the beginning.

Longer (and nerdier) answer

Elsewhere in that same file, you’ll see a reference to DOM.scry:

/**
 * Todo: Support the entire DOM.scry query syntax. For now, these simple
 * utilities will suffice for testing purposes.
 * @lends ReactTestUtils
 */

zpao explains in a comment on a GitHub issue:

That’s a reference to an internal Facebook module. It’s basically querySelectorAll with fallback behavior for handling old browsers and special cases. It is pretty unremarkable and doesn’t actually translate super well here (except maybe a scryRenderedDOMComponentsWithQSA or something, but meh). We’re working on improving the testing in other ways so I don’t think there’s anything we really want to do with this right now.

jimfb takes it a bit further in another GitHub issue, explaining that the name is a reference to Dungeons & Dragons:

Back in the day, we had a bunch of D&D fans on the team.

For reference:
http://www.dandwiki.com/wiki/SRD:Scrying
http://www.dandwiki.com/wiki/SRD3e:Scry_Skill
https://en.wikipedia.org/wiki/Scrying

Historically, we’ve used scry to indicate a helper that finds a set of results. As the framework matures, we should start choosing function names based on what the functions actually do instead of fantasy words that have very little meaning to the typical developer.

Though I would agree that the word has very little meaning to most, it’s worth noting that “scry” is a real English word:

scry
[skrahy]

verb (used without object), scried, scrying.

1. to use divination to discover hidden knowledge or future events, especially by means of a crystal ball.

Interestingly, according to the data from Google’s Ngram Viewer, it seems that the word fell out of normal usage in the early 19th century and then wallowed in obscurity until the 1980s, presumably after D&D gained popularity:

So I can’t say I object to jimfb calling it a “fantasy word”, especially considering the kind of imagery my imagination conjures up when I hear it.