How do I declare expectations about test output (echo, print, etc.)?

[paulshryock]

How do I test output from a function?

/**
 * Prints "something".
 *
 * @return void
 */
function printSomething(): void {
  echo 'something';
}

it('should print "something"', function() {
  printSomething();

  $this->expectOutputRegex('/something/i');
});

// Failed asserting that '' matches PCRE pattern "/something/i".