diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..c20c2ab
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+__pycache__
+
diff --git a/README.md b/fifth/README.md
similarity index 58%
rename from README.md
rename to fifth/README.md
index 4bf3365..d8a776c 100644
--- a/README.md
+++ b/fifth/README.md
@@ -20,26 +20,38 @@ python fifth.py
 ### Example
 
 ```
-stack is: []
-PUSH 10
-stack is: [10]
-PUSH 5
-stack is: [10, 5]
+stack is []
+PUSH 3
+stack is [3]
+PUSH 11
+stack is [3, 11]
 +
-stack is: [15]
-PUSH 45
-stack is: [15, 45]
+stack is [14]
+DUP
+stack is [14, 14]
+PUSH 2
+stack is [14, 14, 2]
+*
+stack is [14, 28]
+SWAP
+stack is [28, 14]
 /
-stack is: [3]
+stack is [2]
++
+ERROR: two numbers required
+POP
+stack is []
 EXIT
 ```
 
 ## Tests
 
 ```bash
-python -m pytest test_stack_calculator.py
+pip install pytest
+pytest -v test_fifth.py
 ```
 
 ## Requirements
 
 - Python 3.10+
+- pytest
diff --git a/fifth.py b/fifth/fifth.py
similarity index 95%
rename from fifth.py
rename to fifth/fifth.py
index 0f6cda7..6cb7088 100644
--- a/fifth.py
+++ b/fifth/fifth.py
@@ -82,9 +82,9 @@ def main():
     fifth = FifthStack()
 
     while True:
-        print(f"stack is: {fifth.stack}")
+        print(f"stack is {fifth.stack}")
         try:
-            if command := input().strip().lower() == "exit":
+            if (command := input().strip().lower()) == "exit":
                 break
             if command:
                 fifth.execute(command)
diff --git a/fifth/requirements.txt b/fifth/requirements.txt
new file mode 100644
index 0000000..8e0e884
--- /dev/null
+++ b/fifth/requirements.txt
@@ -0,0 +1 @@
+pytest==8.4.1
diff --git a/fifth/test_fifth.py b/fifth/test_fifth.py
new file mode 100644
index 0000000..c70433d
--- /dev/null
+++ b/fifth/test_fifth.py
@@ -0,0 +1,166 @@
+import pytest
+from fifth import FifthStack
+
+
+# Test the functions
+def test_push_and_pop():
+    stack = FifthStack()
+    stack.push(10)
+    stack.push(20)
+    assert stack.stack == [10, 20]
+    stack.pop()
+    assert stack.stack == [10]
+    stack.pop()
+    assert stack.stack == []
+
+
+def test_push_invalid_value(capsys):
+    stack = FifthStack()
+    stack.push("abc")
+    captured = capsys.readouterr()
+    assert "ERROR: integer required" in captured.out
+    assert stack.stack == []
+
+
+def test_pop_empty_stack(capsys):
+    stack = FifthStack()
+    stack.pop()
+    captured = capsys.readouterr()
+    assert "ERROR: stack empty" in captured.out
+
+
+def test_swap():
+    stack = FifthStack()
+    stack.push(1)
+    stack.push(2)
+    stack.swap()
+    assert stack.stack == [2, 1]
+
+
+def test_swap_insufficient_elements(capsys):
+    stack = FifthStack()
+    stack.push(1)
+    stack.swap()
+    captured = capsys.readouterr()
+    assert "ERROR: two numbers required" in captured.out
+    assert stack.stack == [1]
+
+
+def test_dup():
+    stack = FifthStack()
+    stack.push(5)
+    stack.dup()
+    assert stack.stack == [5, 5]
+
+
+def test_dup_empty_stack(capsys):
+    stack = FifthStack()
+    stack.dup()
+    captured = capsys.readouterr()
+    assert "ERROR: stack empty" in captured.out
+
+
+def test_addition():
+    stack = FifthStack()
+    stack.push(2)
+    stack.push(3)
+    stack.execute("+")
+    assert stack.stack == [5]
+
+
+def test_subtraction():
+    stack = FifthStack()
+    stack.push(5)
+    stack.push(2)
+    stack.execute("-")
+    assert stack.stack == [3]
+
+
+def test_multiplication():
+    stack = FifthStack()
+    stack.push(4)
+    stack.push(3)
+    stack.execute("*")
+    assert stack.stack == [12]
+
+
+def test_division():
+    stack = FifthStack()
+    stack.push(8)
+    stack.push(2)
+    stack.execute("/")
+    assert stack.stack == [4]
+
+
+def test_division_by_zero(capsys):
+    stack = FifthStack()
+    stack.push(8)
+    stack.push(0)
+    stack.execute("/")
+    captured = capsys.readouterr()
+    assert "ERROR: division by zero" in captured.out
+    assert stack.stack == [8, 0]
+
+
+def test_binary_op_insufficient_elements(capsys):
+    stack = FifthStack()
+    stack.push(1)
+    stack.execute("+")
+    captured = capsys.readouterr()
+    assert "ERROR: two numbers required" in captured.out
+    assert stack.stack == [1]
+
+
+# Test executions
+def test_execute_unknown_command(capsys):
+    stack = FifthStack()
+    stack.execute("foobar")
+    captured = capsys.readouterr()
+    assert "ERROR: unknown command" in captured.out
+
+
+def test_execute_push_command():
+    stack = FifthStack()
+    stack.execute("push 42")
+    assert stack.stack == [42]
+
+
+def test_execute_pop_command():
+    stack = FifthStack()
+    stack.push(99)
+    stack.execute("pop")
+    assert stack.stack == []
+
+
+def test_execute_swap_command():
+    stack = FifthStack()
+    stack.push(1)
+    stack.push(2)
+    stack.execute("swap")
+    assert stack.stack == [2, 1]
+
+
+def test_execute_dup_command():
+    stack = FifthStack()
+    stack.push(7)
+    stack.execute("dup")
+    assert stack.stack == [7, 7]
+
+
+# Test edge cases
+def test_execute_empty_command():
+    stack = FifthStack()
+    stack.execute("")  # Should do nothing
+    assert stack.stack == []
+
+
+def test_execute_whitespace_command():
+    stack = FifthStack()
+    stack.execute("   ")  # Should do nothing
+    assert stack.stack == []
+
+
+def test_case_insensitivity():
+    stack = FifthStack()
+    stack.execute("PUSH 42")
+    assert stack.stack == [42]