scripts/jest/matchers/toWarnDev: Expected and actual arguments to jest-diff are mixed up.

[sompylasar]

Do you want to request a feature or report a bug?

bug

What is the current behavior?

toWarnDev calls jestDiff(a, b) as jestDiff(normalizedMessage, expectedMessages[0]) and jestDiff([normalizedMessage], expectedMessages):

react/scripts/jest/matchers/toWarnDev.js

Lines 49 to 57 in 94518b0

	} else if (expectedMessages.length === 1) {
	errorMessage =
	'Unexpected warning recorded: ' +
	jestDiff(normalizedMessage, expectedMessages[0]);
	} else {
	errorMessage =
	'Unexpected warning recorded: ' +
	jestDiff([normalizedMessage], expectedMessages);
	}

jestDiff(a, b) calls diffStrings(a, b) where by default a is annotated as 'Expected' (green), b as 'Received' (red).

https://github.com/facebook/jest/blob/457776b2889a9be1ce8a2c636a23417264a98d99/packages/jest-diff/src/diff_strings.js#L86-L90

const getAnnotation = (options: ?DiffOptions): string =>
  chalk.green('- ' + ((options && options.aAnnotation) || 'Expected')) +
  '\n' +
  chalk.red('+ ' + ((options && options.bAnnotation) || 'Received')) +
  '\n\n';

What is the expected behavior?

toWarnDev should pass the expected values into a, the actual (received) values into b of jestDiff:

jestDiff(expectedMessages[0], normalizedMessage)

jestDiff(expectedMessages, [normalizedMessage])