fix tests

Author: Fil

src/marks/bar.js

@@ -1,6 +1,6 @@
 import {create} from "d3";
 import {filter} from "../defined.js";
-import {Mark, number, maybeColor, maybeZero, title, maybeNumber} from "../mark.js";
+import {Mark, identity, number, maybeColor, maybeZero, title, maybeNumber} from "../mark.js";
 import {Style, applyDirectStyles, applyIndirectStyles, applyTransform, impliedString, applyAttr} from "../style.js";
 import {stackX, stackY} from "../transforms/stack.js";