import std.array;
assert(withDefaultExtension("file", "ext").array == "file.ext");
assert(withDefaultExtension("file"w, ".ext").array == "file.ext"w);
assert(withDefaultExtension("file.", "ext").array == "file.");
assert(withDefaultExtension("file", "").array == "file.");

import std.utf : byChar, byWchar;
assert(withDefaultExtension("file".byChar, "ext").array == "file.ext");
assert(withDefaultExtension("file"w.byWchar, ".ext").array == "file.ext"w);
assert(withDefaultExtension("file.".byChar, "ext"d).array == "file.");
assert(withDefaultExtension("file".byChar, "").array == "file.");