pub interface ReaderWriter {
    read(mut buf []u8) ?int // from Reader
    write(buf []u8) ?int    // from Writer
}

interface Speaker {
    // first
    speak() string
    // between
    foo() string
    foo2() string
    // last
}

interface Baz {
    // first
    speak() string
    // comment
    // more between
    foo() string
    foo2() string
    // last
}

interface Bar {
    speak() string // after
    foo() string
    speak2() string // also after
    // and between
    foo2() string
}

interface TestsRunner {
mut:
    fn_passes     u64
    fn_fails      u64
    assert_passes u64
    assert_fails  u64
    test_fn_info  &TestFnMetaInfo // filled in by generated code, before .fn_start() is called.
    start(ntests int) // called before all tests, you can initialise private data here. ntests is the number of test functions in the _test.v file.
    finish()          // called after all tests are finished, you should free all the private data here.
    //
    fn_start() // called at the start of each test_ function
    fn_pass()  // called at the end of each test_ function, with no failed assertion
    fn_error(line_nr int, file string, mod string, fn_name string, errmsg string) // called only for `fn test_xyz() ? { return error('message') }`
    fn_fail() // called at the end of each test_ function, with a failed assertion, *or* returning an error
    //
    assert_pass(i &AssertMetaInfo) // called for each `assert true`
    assert_fail(i &AssertMetaInfo) // called for each `assert false`
}