geomLine

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;

assert(gl.front.xTickLabels.empty);
assert(gl.front.yTickLabels.empty);

assertEqual(gl.front.colours[0][1], "a");
assertEqual(gl.front.bounds.min_x, 1.0);
assertEqual(gl.front.bounds.max_x, 1.1);
gl.popFront;
assertEqual(gl.front.colours[0][1], "b");
assertEqual(gl.front.bounds.max_x, 3.0);
gl.popFront;
assert(gl.empty);