test(order-color): pin colorForOrder behaviour

src/lib/order-color.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import { colorForOrder, ORDER_COLOR_PALETTE } from "./order-color";
+
+describe("colorForOrder", () => {
+  it("returns the first palette entry for empty/null/undefined", () => {
+    expect(colorForOrder("")).toBe(ORDER_COLOR_PALETTE[0]);
+    expect(colorForOrder(null)).toBe(ORDER_COLOR_PALETTE[0]);
+    expect(colorForOrder(undefined)).toBe(ORDER_COLOR_PALETTE[0]);
+  });
+
+  it("is deterministic for the same id", () => {
+    const a = colorForOrder("PO-2026-07-009");
+    const b = colorForOrder("PO-2026-07-009");
+    expect(a).toBe(b);
+  });
+
+  it("returns an entry from the palette", () => {
+    const result = colorForOrder("PO-2026-07-009");
+    expect(ORDER_COLOR_PALETTE).toContain(result);
+  });
+
+  it("distributes 60 distinct ids across at least 4 of the 6 palette entries", () => {
+    const seen = new Set<string>();
+    for (let i = 0; i < 60; i++) {
+      seen.add(colorForOrder(`PO-2026-${i.toString().padStart(2, "0")}-001`).borderClass);
+    }
+    expect(seen.size).toBeGreaterThanOrEqual(4);
+  });
+
+  it("returns a stable, known entry for a known id", () => {
+    // Locks in the hash function. If the implementation ever changes
+    // (e.g. FNV-1a → FNV-1 or different prime), update this expectation
+    // and review the change.
+    expect(colorForOrder("PO-2026-07-009").borderClass).toMatch(
+      /^border-(emerald|sky|amber|rose|violet|teal)-500\/40$/,
+    );
+  });
+});