The actual String value for the button might not be visible through button.value.
I find sometimes I'll have to go into button.staticTexts(@"New VC").value or something to find it. Try playing around with it.
I just wanted to add that using XCTAssertEqual to compare strings is not ideal. I found that the binary data is not equal so it returns an error even though the strings match. You'll have to using native Objective C String comparison methods to compare strings then Assert success.
This question is old, but in case it helps anybody, the text on the button can be accessed as follows:
And can be compared against expected string as
XCTAssert([buttons[@"Accessibility Identifier"].label isEqualToString:anotherString]);
Hope this helps someone