adding monkeytype

packages/util/__test__/predicates.spec.ts

@@ -0,0 +1,41 @@
+import { describe, it, expect } from "vitest";
+import { not } from "../src/predicates";
+
+describe("predicates", () => {
+  describe("not", () => {
+    it("should not a simple boolean function", () => {
+      const isTrue = (): boolean => true;
+      const isFalse = not(isTrue);
+
+      expect(isFalse()).toBe(false);
+    });
+
+    it("should not a numeric predicate", () => {
+      const isPositive = (num: number): boolean => num > 0;
+      const isNotPositive = not(isPositive);
+
+      expect(isNotPositive(-5)).toBe(true);
+      expect(isNotPositive(10)).toBe(false);
+    });
+
+    it("should not a predicate taking multiple arguments", () => {
+      const containsLetter = (
+        str1: string,
+        str2: string,
+        letter: string,
+      ): boolean => str1.includes(letter) || str2.includes(letter);
+      const doesNotContainLetter = not(containsLetter);
+
+      expect(doesNotContainLetter("hello", "world", "x")).toBe(true);
+      expect(doesNotContainLetter("apple", "banana", "a")).toBe(false);
+    });
+
+    it("should preserve type safety", () => {
+      const isEven = (num: number): boolean => num % 2 === 0;
+      const isOdd = not(isEven);
+
+      expect(isOdd(3)).toBe(true);
+      expect(isOdd(4)).toBe(false);
+    });
+  });
+});