add test for exponential function with negative numbers

test/test_exponent.c

@@ -56,6 +56,19 @@ void test_Exponent_with_positive_number(void){
     TEST_ASSERT_DOUBLE_WITHIN(0.0001, 7.389056, r3);
 }
 
+void test_Exponent_with_negative_number(void){
+    double r1, r2, r3;
+
+    r1 = exponential(-1.0);
+    r2 = exponential(-2.0);
+
+    printf("Result 1: %lf\n", r1);
+    printf("Result 2: %lf\n", r2);
+
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.367879, r1);
+    TEST_ASSERT_DOUBLE_WITHIN(0.000001, 0.135335, r2);
+}
+
 
 
 #endif // TEST