Macro assert_diagnostic_lines

macro_rules! assert_diagnostic_lines {
    ($diagnostic:expr, $($expected_lines:expr),+) => { ... };
}

Like assert_diagnostic, but matches each non-empty line of the rendered output to a corresponding pattern.

So if the output has 3 lines, the second of which is empty, and you provide 2 patterns, the assertion passes if the first line matches the first pattern, and the third line matches the second pattern - the second line is ignored because it is empty.