Units separated to their own block, and properly tested

src/units.js

@@ -0,0 +1,21 @@
+const a = require('./assert')
+const prep = require('./prepare')
+
+const default_units = {
+    u: 19,
+    cx: 18,
+    cy: 17
+}
+
+exports.parse = (config = {}) => {
+    const raw_units = prep.extend(
+        default_units,
+        a.sane(config.units || {}, 'units', 'object')(),
+        a.sane(config.variables || {}, 'variables', 'object')()
+    )
+    const units = {}
+    for (const [key, val] of Object.entries(raw_units)) {
+        units[key] = a.mathnum(val)(units)
+    }
+    return units
+}