From 4dff67c94b463f8de400d9be6274d2dc4f205148 Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Tue, 22 Jul 2025 21:28:12 +0200
Subject: [PATCH 1/5] testing: improve test coverage NodeStackTest

---
 .../datastructures/stacks/NodeStackTest.java  | 181 +++++++++++++++++-
 1 file changed, 180 insertions(+), 1 deletion(-)

diff --git a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
index 7ac0d8bc324b..5e944cb6fcf2 100644
--- a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
@@ -4,12 +4,25 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
 
 class NodeStackTest {
 
+    private NodeStack<Integer> intStack;
+    private NodeStack<String> stringStack;
+
+    @BeforeEach
+    void setUp() {
+        intStack = new NodeStack<>();
+        stringStack = new NodeStack<>();
+    }
+
     @Test
+    @DisplayName("Test push operation")
     void testPush() {
         NodeStack<Integer> stack = new NodeStack<>();
         stack.push(10);
@@ -18,6 +31,7 @@ void testPush() {
     }
 
     @Test
+    @DisplayName("Test pop operation")
     void testPop() {
         NodeStack<String> stack = new NodeStack<>();
         stack.push("First");
@@ -27,12 +41,14 @@ void testPop() {
     }
 
     @Test
+    @DisplayName("Test pop on empty stack throws exception")
     void testPopOnEmptyStack() {
         NodeStack<Double> stack = new NodeStack<>();
         assertThrows(IllegalStateException.class, stack::pop, "Popping an empty stack should throw IllegalStateException.");
     }
 
     @Test
+    @DisplayName("Test peek operation")
     void testPeek() {
         NodeStack<Integer> stack = new NodeStack<>();
         stack.push(5);
@@ -43,12 +59,14 @@ void testPeek() {
     }
 
     @Test
+    @DisplayName("Test peek on empty stack throws exception")
     void testPeekOnEmptyStack() {
         NodeStack<String> stack = new NodeStack<>();
         assertThrows(IllegalStateException.class, stack::peek, "Peeking an empty stack should throw IllegalStateException.");
     }
 
     @Test
+    @DisplayName("Test isEmpty method")
     void testIsEmpty() {
         NodeStack<Character> stack = new NodeStack<>();
         assertTrue(stack.isEmpty(), "Newly initialized stack should be empty.");
@@ -59,6 +77,7 @@ void testIsEmpty() {
     }
 
     @Test
+    @DisplayName("Test size method")
     void testSize() {
         NodeStack<Integer> stack = new NodeStack<>();
         assertEquals(0, stack.size(), "Size of empty stack should be 0.");
@@ -70,4 +89,164 @@ void testSize() {
         stack.pop();
         assertEquals(0, stack.size(), "Size should be 0 after popping all elements.");
     }
-}
+
+    @Test
+    @DisplayName("Test push and pop with null values")
+    void testPushPopWithNull() {
+        stringStack.push(null);
+        stringStack.push("not null");
+        stringStack.push(null);
+
+        assertEquals(3, stringStack.size(), "Stack should contain 3 elements including nulls");
+        assertNull(stringStack.pop(), "Should pop null value");
+        assertEquals("not null", stringStack.pop(), "Should pop 'not null' value");
+        assertNull(stringStack.pop(), "Should pop null value");
+        assertTrue(stringStack.isEmpty(), "Stack should be empty after popping all elements");
+    }
+
+    @Test
+    @DisplayName("Test LIFO (Last In First Out) behavior")
+    void testLifoBehavior() {
+        int[] values = {1, 2, 3, 4, 5};
+
+        // Push values in order
+        for (int value : values) {
+            intStack.push(value);
+        }
+
+        // Pop values should be in reverse order
+        for (int i = values.length - 1; i >= 0; i--) {
+            assertEquals(values[i], intStack.pop(), "Elements should be popped in LIFO order");
+        }
+    }
+
+    @Test
+    @DisplayName("Test peek doesn't modify stack")
+    void testPeekDoesNotModifyStack() {
+        intStack.push(1);
+        intStack.push(2);
+        intStack.push(3);
+
+        int originalSize = intStack.size();
+        int peekedValue = intStack.peek();
+
+        assertEquals(3, peekedValue, "Peek should return top element");
+        assertEquals(originalSize, intStack.size(), "Peek should not change stack size");
+        assertEquals(3, intStack.peek(), "Multiple peeks should return same value");
+        assertFalse(intStack.isEmpty(), "Peek should not make stack empty");
+    }
+
+    @Test
+    @DisplayName("Test mixed push and pop operations")
+    void testMixedOperations() {
+        // Test interleaved push/pop operations
+        intStack.push(1);
+        assertEquals(1, intStack.pop());
+        assertTrue(intStack.isEmpty());
+
+        intStack.push(2);
+        intStack.push(3);
+        assertEquals(3, intStack.pop());
+        intStack.push(4);
+        assertEquals(4, intStack.peek());
+        assertEquals(2, intStack.size());
+
+        assertEquals(4, intStack.pop());
+        assertEquals(2, intStack.pop());
+        assertTrue(intStack.isEmpty());
+    }
+
+    @Test
+    @DisplayName("Test stack with duplicate values")
+    void testStackWithDuplicates() {
+        intStack.push(1);
+        intStack.push(1);
+        intStack.push(1);
+
+        assertEquals(3, intStack.size(), "Stack should handle duplicate values");
+        assertEquals(1, intStack.peek(), "Peek should return duplicate value");
+
+        assertEquals(1, intStack.pop(), "Should pop first duplicate");
+        assertEquals(1, intStack.pop(), "Should pop second duplicate");
+        assertEquals(1, intStack.pop(), "Should pop third duplicate");
+        assertTrue(intStack.isEmpty(), "Stack should be empty after popping all duplicates");
+    }
+
+    @Test
+    @DisplayName("Test stack with different data types")
+    void testDifferentDataTypes() {
+        NodeStack<Character> charStack = new NodeStack<>();
+        NodeStack<Boolean> booleanStack = new NodeStack<>();
+
+        // Test with Character
+        charStack.push('A');
+        charStack.push('Z');
+        assertEquals('Z', charStack.peek(), "Should handle Character values");
+
+        // Test with Boolean
+        booleanStack.push(true);
+        booleanStack.push(false);
+        assertEquals(false, booleanStack.peek(), "Should handle Boolean values");
+    }
+
+    @Test
+    @DisplayName("Test stack state consistency after exceptions")
+    void testStateConsistencyAfterExceptions() {
+        // Stack should remain consistent after exception-throwing operations
+        intStack.push(1);
+        intStack.push(2);
+
+        // Try to peek and pop normally first
+        assertEquals(2, intStack.peek());
+        assertEquals(2, intStack.pop());
+        assertEquals(1, intStack.size());
+
+        // Pop remaining element
+        assertEquals(1, intStack.pop());
+        assertTrue(intStack.isEmpty());
+
+        // Now stack is empty, operations should throw exceptions
+        assertThrows(IllegalStateException.class, intStack::peek);
+        assertThrows(IllegalStateException.class, intStack::pop);
+
+        // Stack should still be in valid empty state
+        assertTrue(intStack.isEmpty());
+        assertEquals(0, intStack.size());
+
+        // Should be able to push after exceptions
+        intStack.push(3);
+        assertFalse(intStack.isEmpty());
+        assertEquals(1, intStack.size());
+        assertEquals(3, intStack.peek());
+    }
+
+    @Test
+    @DisplayName("Test single element stack operations")
+    void testSingleElementStack() {
+        intStack.push(2);
+
+        assertFalse(intStack.isEmpty(), "Stack with one element should not be empty");
+        assertEquals(1, intStack.size(), "Size should be 1");
+        assertEquals(2, intStack.peek(), "Peek should return the single element");
+        assertEquals(1, intStack.size(), "Peek should not change size");
+
+        assertEquals(2, intStack.pop(), "Pop should return the single element");
+        assertTrue(intStack.isEmpty(), "Stack should be empty after popping single element");
+        assertEquals(0, intStack.size(), "Size should be 0 after popping single element");
+    }
+
+    @Test
+    @DisplayName("Test toString method if implemented")
+    void testToString() {
+        // This test assumes NodeStack has a toString method
+        // If not implemented, this test can be removed or NodeStack can be enhanced
+        intStack.push(1);
+        intStack.push(2);
+        intStack.push(3);
+
+        String stackString = intStack.toString();
+        // Basic check that toString doesn't throw exception and returns something
+        assertTrue(stackString != null, "toString should not return null");
+        assertTrue(stackString.length() > 0, "toString should return non-empty string");
+    }
+}
\ No newline at end of file

From fc7f16ac07c50fbeb0a1280e2800b265e682e450 Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Tue, 22 Jul 2025 21:31:38 +0200
Subject: [PATCH 2/5] style: fix style issues

---
 .../thealgorithms/datastructures/stacks/NodeStackTest.java  | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
index 5e944cb6fcf2..14db5632ef71 100644
--- a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
@@ -2,13 +2,13 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
-import static org.junit.jupiter.api.Assertions.assertNull;
 
-import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
 
 class NodeStackTest {
 
@@ -249,4 +249,4 @@ void testToString() {
         assertTrue(stackString != null, "toString should not return null");
         assertTrue(stackString.length() > 0, "toString should return non-empty string");
     }
-}
\ No newline at end of file
+}

From 7e75cf3e1f2e4cc637829f39fa8dab2037f0ae67 Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Tue, 22 Jul 2025 21:36:18 +0200
Subject: [PATCH 3/5] testing: fix type

---
 .../thealgorithms/datastructures/stacks/NodeStackTest.java  | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
index 14db5632ef71..cb212ed1b784 100644
--- a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
@@ -184,9 +184,9 @@ void testDifferentDataTypes() {
         assertEquals('Z', charStack.peek(), "Should handle Character values");
 
         // Test with Boolean
-        booleanStack.push(true);
-        booleanStack.push(false);
-        assertEquals(false, booleanStack.peek(), "Should handle Boolean values");
+        booleanStack.push(Boolean.TRUE);
+        booleanStack.push(Boolean.FALSE);
+        assertEquals(Boolean.FALSE, booleanStack.peek(), "Should handle Boolean values");
     }
 
     @Test

From 72bc426bed299d738196e31dc6b52ed4f5fdc68b Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Tue, 22 Jul 2025 21:43:00 +0200
Subject: [PATCH 4/5] testing: fix import

---
 .../thealgorithms/datastructures/stacks/NodeStackTest.java   | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
index cb212ed1b784..7e9f3750acbd 100644
--- a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
@@ -2,7 +2,6 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -98,9 +97,9 @@ void testPushPopWithNull() {
         stringStack.push(null);
 
         assertEquals(3, stringStack.size(), "Stack should contain 3 elements including nulls");
-        assertNull(stringStack.pop(), "Should pop null value");
+        org.junit.jupiter.api.Assertions.assertNull(stringStack.pop(), "Should pop null value");
         assertEquals("not null", stringStack.pop(), "Should pop 'not null' value");
-        assertNull(stringStack.pop(), "Should pop null value");
+        org.junit.jupiter.api.Assertions.assertNull(stringStack.pop(), "Should pop null value");
         assertTrue(stringStack.isEmpty(), "Stack should be empty after popping all elements");
     }
 

From 9ac4d8e50a45f58526de6d3435262e9066edd163 Mon Sep 17 00:00:00 2001
From: alxkm <alexanderklmn@gmail.com>
Date: Tue, 22 Jul 2025 21:44:01 +0200
Subject: [PATCH 5/5] testing: fix import

---
 .../datastructures/stacks/NodeStackTest.java             | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
index 7e9f3750acbd..8a89382211ba 100644
--- a/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/stacks/NodeStackTest.java
@@ -1,7 +1,6 @@
 package com.thealgorithms.datastructures.stacks;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -70,7 +69,7 @@ void testIsEmpty() {
         NodeStack<Character> stack = new NodeStack<>();
         assertTrue(stack.isEmpty(), "Newly initialized stack should be empty.");
         stack.push('A');
-        assertFalse(stack.isEmpty(), "Stack should not be empty after a push operation.");
+        org.junit.jupiter.api.Assertions.assertFalse(stack.isEmpty(), "Stack should not be empty after a push operation.");
         stack.pop();
         assertTrue(stack.isEmpty(), "Stack should be empty after popping the only element.");
     }
@@ -132,7 +131,7 @@ void testPeekDoesNotModifyStack() {
         assertEquals(3, peekedValue, "Peek should return top element");
         assertEquals(originalSize, intStack.size(), "Peek should not change stack size");
         assertEquals(3, intStack.peek(), "Multiple peeks should return same value");
-        assertFalse(intStack.isEmpty(), "Peek should not make stack empty");
+        org.junit.jupiter.api.Assertions.assertFalse(intStack.isEmpty(), "Peek should not make stack empty");
     }
 
     @Test
@@ -214,7 +213,7 @@ void testStateConsistencyAfterExceptions() {
 
         // Should be able to push after exceptions
         intStack.push(3);
-        assertFalse(intStack.isEmpty());
+        org.junit.jupiter.api.Assertions.assertFalse(intStack.isEmpty());
         assertEquals(1, intStack.size());
         assertEquals(3, intStack.peek());
     }
@@ -224,7 +223,7 @@ void testStateConsistencyAfterExceptions() {
     void testSingleElementStack() {
         intStack.push(2);
 
-        assertFalse(intStack.isEmpty(), "Stack with one element should not be empty");
+        org.junit.jupiter.api.Assertions.assertFalse(intStack.isEmpty(), "Stack with one element should not be empty");
         assertEquals(1, intStack.size(), "Size should be 1");
         assertEquals(2, intStack.peek(), "Peek should return the single element");
         assertEquals(1, intStack.size(), "Peek should not change size");

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