Assistant: 
User: System: You are in a role play game. The following roles are available:
                Admin: Call this Agent if:
        You need guidance.
        The program is not working as expected.
        You need api key
        DO NOT CALL THIS AGENT IF:
        You need to execute the code.
Developer: Call this Agent if:   
        You need to write code.                  
        DO NOT CALL THIS AGENT IF:  
        You need to execute the code.
Quality_assurance: You are an AI Quality Assurance. Follow these instructions:
      0.ВСЕГДА ГОВОРИ НА РУССКОМ ЯЗЫКЕ
      1. Double check the plan, 
      2. if there's a bug or error suggest a resolution
      3. If the task is not solved, analyze the problem, revisit your assumption, collect additional info you need, and think of a different approach..
                Read the following conversation.
                Then select the next role from ['Admin', 'Developer', 'Quality_assurance'] to play. Only return the role.
User: Разработка по TDD. Напишите функцию - обход графа в глубину.
User: Sure! Here’s a simple implementation of a depth-first search (DFS) function for traversing a graph using Test-Driven Development (TDD) principles. 

### Step 1: Write the Test

First, we need to define a test for our DFS function. Here’s an example using Python's `unittest` framework:

```python
import unittest

class TestGraphTraversal(unittest.TestCase):
    def test_dfs(self):
        graph = {
            'A': ['B', 'C'],
            'B': ['D'],
            'C': ['E'],
            'D': [],
            'E': []
        }
        expected_output = ['A', 'B', 'D', 'C', 'E']
        self.assertEqual(dfs(graph, 'A'), expected_output)

def dfs(graph, start):
    # This will be implemented next
    pass

if __name__ == '__main__':
    unittest.main()
```

### Step 2: Implement the Function

Now, let’s implement the `dfs` function to pass the test:

```python
def dfs(graph, start, visited=None):
    if visited is None:
        visited = []
    visited.append(start)
    for neighbor in graph[start]:
        if neighbor not in visited:
            dfs(graph, neighbor, visited)
    return visited
```

### Step 3: Run the Test

Now, you can run the test to ensure that the DFS function works as expected. If everything is set up correctly, the test should pass, confirming that the function behaves as intended.

### Final Code

Here’s the complete code:

```python
import unittest

def dfs(graph, start, visited=None):
    if visited is None:
        visited = []
    visited.append(start)
    for neighbor in graph[start]:
        if neighbor not in visited:
            dfs(graph, neighbor, visited)
    return visited

class TestGraphTraversal(unittest.TestCase):
    def test_dfs(self):
        graph = {
            'A': ['B', 'C'],
            'B': ['D'],
            'C': ['E'],
            'D': [],
            'E': []
        }
        expected_output = ['A', 'B', 'D', 'C', 'E']
        self.assertEqual(dfs(graph, 'A'), expected_output)

if __name__ == '__main__':
    unittest.main()
```

This implementation follows TDD principles by first writing a test case and then
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