tests: added some test to sorting algorithm (#222)

## Pull Request type

Following the recent issue on bubble sort, I added some test to sorting
algorithms

Please check the type of change your PR introduces:

- [ ] Bugfix
- [ ] Feature
- [ ] Code style update (formatting, renaming)
- [ ] Refactoring (no functional changes, no API changes)
- [ ] Build-related changes
- [ ] Documentation content changes
- [X] Other (please describe): unit tests

## What is the current behavior?

Issue Number: N/A

## What is the new behavior?

- Test covers more scenarios

## Does this introduce a breaking change?

- [ ] Yes
- [X] No

## Other information

src/sorting/src/tests/bubble_sort_test.cairo

@@ -47,11 +47,33 @@ fn bubblesort_test_pre_sorted() {
 
 #[test]
 #[available_gas(2000000)]
-fn bubblesort_test_2_same_values() {
+fn bubblesort_test_pre_sorted_decreasing() {
+    let mut data = array![4_u32, 3_u32, 2_u32, 1_u32];
+    let mut correct = array![1_u32, 2_u32, 3_u32, 4_u32];
+
+    let sorted = bubble_sort::bubble_sort_elements(data);
+
+    assert(is_equal(sorted.span(), correct.span()), 'invalid result');
+}
+
+#[test]
+#[available_gas(2000000)]
+fn bubblesort_test_pre_sorted_2_same_values() {
     let mut data = array![1_u32, 2_u32, 2_u32, 4_u32];
     let mut correct = array![1_u32, 2_u32, 2_u32, 4_u32];
 
     let sorted = bubble_sort::bubble_sort_elements(data);
 
     assert(is_equal(sorted.span(), correct.span()), 'invalid result');
 }
+
+#[test]
+#[available_gas(2000000)]
+fn bubblesort_test_2_same_values() {
+    let mut data = array![1_u32, 2_u32, 4_u32, 2_u32];
+    let mut correct = array![1_u32, 2_u32, 2_u32, 4_u32];
+
+    let sorted = bubble_sort::bubble_sort_elements(data);
+
+    assert(is_equal(sorted.span(), correct.span()), 'invalid result');
+}

src/sorting/src/tests/merge_sort_test.cairo

@@ -11,6 +11,17 @@ fn mergesort_test() {
     assert(is_equal(sorted, correct), 'invalid result');
 }
 
+#[test]
+#[available_gas(2000000)]
+fn mergesort_test_2_pre_sorted_decreasing() {
+    let mut data = array![4_u32, 3_u32, 2_u32, 1_u32];
+    let mut correct = array![1_u32, 2_u32, 3_u32, 4_u32];
+
+    let sorted = merge(data);
+
+    assert(is_equal(sorted.span(), correct.span()), 'invalid result');
+}
+
 #[test]
 #[available_gas(2000000)]
 fn mergesort_test_empty() {
@@ -44,3 +55,25 @@ fn mergesort_test_pre_sorted() {
 
     assert(is_equal(sorted.span(), correct.span()), 'invalid result');
 }
+
+#[test]
+#[available_gas(2000000)]
+fn mergesort_test_2_same_values() {
+    let mut data = array![1_u32, 2_u32, 3_u32, 2_u32, 4_u32];
+    let mut correct = array![1_u32, 2_u32, 2_u32, 3_u32, 4_u32];
+
+    let sorted = merge(data);
+
+    assert(is_equal(sorted.span(), correct.span()), 'invalid result');
+}
+
+#[test]
+#[available_gas(2000000)]
+fn mergesort_test_2_same_values_pre_sorted() {
+    let mut data = array![1_u32, 2_u32, 2_u32, 3_u32, 4_u32];
+    let mut correct = array![1_u32, 2_u32, 2_u32, 3_u32, 4_u32];
+
+    let sorted = merge(data);
+
+    assert(is_equal(sorted.span(), correct.span()), 'invalid result');
+}