Question

graphs unit test

Answer 1

Creating a unit test for graphs typically involves testing various functionalities of a graph data structure. This could include tests for adding vertices, adding edges, checking for connectivity, finding paths, and more.

Here’s a simple outline of how you might write unit tests for a graph implementation in Python using the `unittest` framework. For the sake of illustration, let's assume you have a simple graph class implementation that supports adding vertices and edges, and you want to test its functionalities.

### Example Graph Implementation (For context)

Before diving into the tests, here's an example implementation of a simple Graph class:

```python
class Graph:
def __init__(self):
self.adjacency_list = {}

def add_vertex(self, vertex):
if vertex not in self.adjacency_list:
self.adjacency_list[vertex] = []

def add_edge(self, start_vertex, end_vertex):
if start_vertex in self.adjacency_list and end_vertex in self.adjacency_list:
self.adjacency_list[start_vertex].append(end_vertex)
self.adjacency_list[end_vertex].append(start_vertex) # For undirected graph

def has_vertex(self, vertex):
return vertex in self.adjacency_list

def get_edges(self, vertex):
return self.adjacency_list.get(vertex, [])

def __str__(self):
return str(self.adjacency_list)
```

### Unit Tests for Graph Class

Here’s a set of unit tests you could write:

```python
import unittest

class TestGraph(unittest.TestCase):
def setUp(self):
# Create a new graph for testing
self.graph = Graph()
self.graph.add_vertex("A")
self.graph.add_vertex("B")
self.graph.add_vertex("C")

def test_add_vertex(self):
self.graph.add_vertex("D")
self.assertTrue(self.graph.has_vertex("D"))
self.assertFalse(self.graph.has_vertex("E"))

def test_add_edge(self):
self.graph.add_edge("A", "B")
self.graph.add_edge("B", "C")
edges_A = self.graph.get_edges("A")
edges_B = self.graph.get_edges("B")

self.assertIn("B", edges_A)
self.assertIn("A", edges_B)
self.assertIn("C", edges_B)

def test_edge_with_nonexistent_vertex(self):
self.graph.add_edge("A", "D") # D does not exist
edges_A = self.graph.get_edges("A")
self.assertNotIn("D", edges_A)

def test_has_vertex(self):
self.assertTrue(self.graph.has_vertex("A"))
self.assertTrue(self.graph.has_vertex("B"))
self.assertFalse(self.graph.has_vertex("D")) # D has not been added yet

def test_get_edges(self):
self.graph.add_edge("A", "B")
self.assertEqual(self.graph.get_edges("A"), ["B"])
self.assertEqual(self.graph.get_edges("B"), ["A"])

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

### Explanation of Tests

1. **setUp**: This method creates a new `Graph` instance and adds vertices "A", "B", and "C" for use in the tests.

2. **test_add_vertex**: Tests that a vertex can be added and that it is indeed added to the graph.

3. **test_add_edge**: Tests that edges are added correctly between vertices and ensures that the edges are bidirectional.

4. **test_edge_with_nonexistent_vertex**: Tests that trying to add an edge with a non-existent vertex does not affect the current vertex's edges.

5. **test_has_vertex**: Tests the `has_vertex` method to ensure it accurately reports the presence or absence of a vertex.

6. **test_get_edges**: Ensures that retrieving edges for a vertex works as expected after adding edges.

### Running the Tests

To run the tests, save the code in a Python file (e.g., `test_graph.py`) and execute the file using Python:

```bash
python test_graph.py
```

This setup should give you a starting point for unit testing your graph implementation. Adjust the tests based on your graph's specific functionalities.