feat: add rate normalization helpers

tests/rate-normalizer.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, test } from "vitest";
+
+import {
+  compareRateValues,
+  normalizeRateDisplay,
+  parseRateLowerBound
+} from "../src/shared/rate-normalizer";
+
+describe("rate-normalizer", () => {
+  test("normalizes compact ranges", () => {
+    expect(normalizeRateDisplay("0.5%-1%")).toBe("0.5% - 1%");
+  });
+
+  test("normalizes ranges with missing percent on the lower bound", () => {
+    expect(normalizeRateDisplay("0.02 - 0.1%")).toBe("0.02% - 0.1%");
+  });
+
+  test("parses the lower bound of a range", () => {
+    expect(parseRateLowerBound("0.02% - 0.1%")).toBe(0.02);
+  });
+
+  test("treats less-than values as smaller than the boundary range", () => {
+    expect(compareRateValues("<0.02%", "0.02% - 0.1%")).toBeLessThan(0);
+  });
+
+  test("orders missing values after real values", () => {
+    expect(compareRateValues(null, "0.02% - 0.1%")).toBeGreaterThan(0);
+  });
+});