Enhance tests for proper fraction validation

Added test cases for negative improper fractions.

Author: CatchingKiyoko

Sprint-3/1-implement-and-rewrite-tests/rewrite-tests-with-jest/2-is-proper-fraction.test.js

@@ -19,4 +19,9 @@ test("should return true for a negative proper fraction", () => {
 // Case 4: Identify Equal Numerator and Denominator:
 test ("should return false when numerator equals denominator", () => {
   expect(isProperFraction(3, 3)).toEqual(false);
-});
+});
+
+// Case 5: Identify Negative Improper Fractions: 
+test("should return false for a negative improper fraction", () => {
+  expect(isProperFraction(-4, 4)).toEqual(false);
+  expect(isProperFraction(10, -3)).toEqual(false);