auto aes = Aes!(double[], "x", double[], "y", string[], "colour")([1.0,
    2.0, 1.1, 3.0], [3.0, 1.5, 1.1, 1.8], ["a", "b", "a", "b"]);

auto gl = geomLine(aes);

import std.range : empty;

assertHasValue([1.0, 2.0], gl.front.xStore.min());
assertHasValue([1.1, 3.0], gl.front.xStore.max());
gl.popFront;
assertHasValue([1.1, 3.0], gl.front.xStore.max());
gl.popFront;
assert(gl.empty);