Add portion controls and improve recipe display

test/recipe-scaler.test.js

@@ -0,0 +1,28 @@
+const test = require("node:test");
+const assert = require("node:assert/strict");
+const { parseYield, scaleIngredient, scaleRecipe } = require("../lib/recipe-scaler");
+
+test("extracts the number of portions from a recipe yield", () => {
+  assert.equal(parseYield("6 servings"), 6);
+  assert.equal(parseYield(4), 4);
+  assert.equal(parseYield("as needed"), null);
+});
+
+test("scales leading whole, fractional, and mixed quantities", () => {
+  assert.equal(scaleIngredient("2 cups oats", 2), "4 cups oats");
+  assert.equal(scaleIngredient("½ cup milk", 2), "1 cup milk");
+  assert.equal(scaleIngredient("1 1/2 tsp salt", 2), "3 tsp salt");
+  assert.equal(scaleIngredient("Salt to taste", 2), "Salt to taste");
+});
+
+test("returns a scaled copy of a recipe", () => {
+  const original = {
+    name: "Oatmeal Cups",
+    recipeYield: "6 servings",
+    recipeIngredient: ["2 cups oats", "Salt to taste"]
+  };
+  const scaled = scaleRecipe(original, 9);
+  assert.equal(scaled.recipeYield, "9 servings");
+  assert.deepEqual(scaled.recipeIngredient, ["3 cups oats", "Salt to taste"]);
+  assert.equal(original.recipeYield, "6 servings");
+});