testing: improve SortStackTest (#6422)

testing: improve SortStackTest

Co-authored-by: Deniz Altunkapan <[email protected]>

Author: alxkm

src/test/java/com/thealgorithms/stacks/SortStackTest.java

@@ -74,4 +74,187 @@ public void testSortWithDuplicateElements() {
         assertEquals(2, (int) stack.pop());
         assertEquals(1, (int) stack.pop());
     }
+
+    @Test
+    public void testSortReverseSortedStack() {
+        // Test worst case scenario - completely reverse sorted
+        stack.push(5);
+        stack.push(4);
+        stack.push(3);
+        stack.push(2);
+        stack.push(1);
+        SortStack.sortStack(stack);
+
+        assertEquals(5, stack.size());
+        assertEquals(5, (int) stack.pop());
+        assertEquals(4, (int) stack.pop());
+        assertEquals(3, (int) stack.pop());
+        assertEquals(2, (int) stack.pop());
+        assertEquals(1, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortWithAllSameElements() {
+        // Test stack with all identical elements
+        stack.push(7);
+        stack.push(7);
+        stack.push(7);
+        stack.push(7);
+        SortStack.sortStack(stack);
+
+        assertEquals(4, stack.size());
+        assertEquals(7, (int) stack.pop());
+        assertEquals(7, (int) stack.pop());
+        assertEquals(7, (int) stack.pop());
+        assertEquals(7, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortWithNegativeNumbers() {
+        // Test with negative numbers
+        stack.push(-3);
+        stack.push(1);
+        stack.push(-5);
+        stack.push(2);
+        stack.push(-1);
+        SortStack.sortStack(stack);
+
+        assertEquals(5, stack.size());
+        assertEquals(2, (int) stack.pop());
+        assertEquals(1, (int) stack.pop());
+        assertEquals(-1, (int) stack.pop());
+        assertEquals(-3, (int) stack.pop());
+        assertEquals(-5, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortWithAllNegativeNumbers() {
+        // Test with only negative numbers
+        stack.push(-10);
+        stack.push(-5);
+        stack.push(-15);
+        stack.push(-1);
+        SortStack.sortStack(stack);
+
+        assertEquals(4, stack.size());
+        assertEquals(-1, (int) stack.pop());
+        assertEquals(-5, (int) stack.pop());
+        assertEquals(-10, (int) stack.pop());
+        assertEquals(-15, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortWithZero() {
+        // Test with zero included
+        stack.push(3);
+        stack.push(0);
+        stack.push(-2);
+        stack.push(1);
+        SortStack.sortStack(stack);
+
+        assertEquals(4, stack.size());
+        assertEquals(3, (int) stack.pop());
+        assertEquals(1, (int) stack.pop());
+        assertEquals(0, (int) stack.pop());
+        assertEquals(-2, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortLargerStack() {
+        // Test with a larger number of elements
+        int[] values = {15, 3, 9, 1, 12, 6, 18, 4, 11, 8};
+        for (int value : values) {
+            stack.push(value);
+        }
+
+        SortStack.sortStack(stack);
+
+        assertEquals(10, stack.size());
+
+        // Verify sorted order (largest to smallest when popping)
+        int[] expectedOrder = {18, 15, 12, 11, 9, 8, 6, 4, 3, 1};
+        for (int expected : expectedOrder) {
+            assertEquals(expected, (int) stack.pop());
+        }
+    }
+
+    @Test
+    public void testSortTwoElements() {
+        // Test edge case with exactly two elements
+        stack.push(5);
+        stack.push(2);
+        SortStack.sortStack(stack);
+
+        assertEquals(2, stack.size());
+        assertEquals(5, (int) stack.pop());
+        assertEquals(2, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortTwoElementsAlreadySorted() {
+        // Test two elements already in correct order
+        stack.push(2);
+        stack.push(5);
+        SortStack.sortStack(stack);
+
+        assertEquals(2, stack.size());
+        assertEquals(5, (int) stack.pop());
+        assertEquals(2, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortStackWithMinAndMaxValues() {
+        // Test with Integer.MAX_VALUE and Integer.MIN_VALUE
+        stack.push(0);
+        stack.push(Integer.MAX_VALUE);
+        stack.push(Integer.MIN_VALUE);
+        stack.push(100);
+        SortStack.sortStack(stack);
+
+        assertEquals(4, stack.size());
+        assertEquals(Integer.MAX_VALUE, (int) stack.pop());
+        assertEquals(100, (int) stack.pop());
+        assertEquals(0, (int) stack.pop());
+        assertEquals(Integer.MIN_VALUE, (int) stack.pop());
+    }
+
+    @Test
+    public void testSortWithManyDuplicates() {
+        // Test with multiple sets of duplicates
+        stack.push(3);
+        stack.push(1);
+        stack.push(3);
+        stack.push(1);
+        stack.push(2);
+        stack.push(2);
+        stack.push(3);
+        SortStack.sortStack(stack);
+
+        assertEquals(7, stack.size());
+        assertEquals(3, (int) stack.pop());
+        assertEquals(3, (int) stack.pop());
+        assertEquals(3, (int) stack.pop());
+        assertEquals(2, (int) stack.pop());
+        assertEquals(2, (int) stack.pop());
+        assertEquals(1, (int) stack.pop());
+        assertEquals(1, (int) stack.pop());
+    }
+
+    @Test
+    public void testOriginalStackIsModified() {
+        // Verify that the original stack is modified, not a copy
+        Stack<Integer> originalReference = stack;
+        stack.push(3);
+        stack.push(1);
+        stack.push(2);
+
+        SortStack.sortStack(stack);
+
+        // Verify it's the same object reference
+        assertTrue(stack == originalReference);
+        assertEquals(3, stack.size());
+        assertEquals(3, (int) stack.pop());
+        assertEquals(2, (int) stack.pop());
+        assertEquals(1, (int) stack.pop());
+    }
 }