Renders every failing assertion of one test: message, values, and source location.

formatFailureBlock([
  { index: 1, message: 'bad sum', actual: 3, expected: 4, stack: null, at: 'lib/math.ts:4:3', source: null },
]);
// 'bad sum\nexpected: 4\nactual:   3\nat lib/math.ts:4:3\n' (message red on a TTY)
formatFailureBlock([]); // ''