The phrase "a test of which" is correct and usable in written English.
It can be used when referring to a specific test related to something previously mentioned, often in a formal or academic context.
Example: "The results of the experiment were a test of which method was more effective in reducing errors."
Alternatives: "a test regarding" or "an assessment of which".
After the rain delay, the game became a test of which bullpen was worse.
Democrats are casting this year's budget fight in Congress as a test of which party can do more to wean the government off of using excess Social Security revenue to pay for general programs.
As a test of which waterways and wetlands might fall under the Clean Water Act, it ruled out those that were completely isolated and whose sole qualification for federal jurisdiction was their use by migratory birds, the one standard the court explicitly rejected.
Barbara Bellantonio East Meadow, N.Y., Oct. 30, 2010 To the Editor: Re "For Democrats, Financial Edge in Campaigns" (front page, Oct. 27): Sad commentary department: The following excerpt from your article about campaign finance: "The battle for control of the House has been increasingly shaping up as a test" of which party can raise more funds.
The women's final at the United States Open is going to be a test of which is the better way to advance through a draw at a major championship: rolling over everyone in your path, or having to dig for every point in grueling victories.
One group took a test of which the first half was presented in oral mode and the rest in written mode.
He was inclined to see the struggle as a test of wills, which he could win by striking a decisive blow, the officials said.
Yet here in Nevada, 129 years after Marx's death, capital and labour are locked in a test of strength which could help determine the presidential election.
Whatever else their relationship involved, it must have included a test of wills, which made it unlike any ordinary office relationship.
It is a face-off, a test of wills, which has left thousands dead and opened a dark chapter in what was initially called the Arab Spring.
"The requirement that if a pupil is to qualify for admission his mother must be Jewish, whether by descent or conversion, is a test of ethnicity which contravenes the Race Relations Act," the court said.
