diff --git a/tests/unit/test_graph_builder.py b/tests/unit/test_graph_builder.py
new file mode 100644
index 0000000..8f77cec
--- /dev/null
+++ b/tests/unit/test_graph_builder.py
@@ -0,0 +1,138 @@
+import pytest
+from pathlib import Path
+from src.graph.builder import GraphBuilder, GraphType, GraphNode, NodeType, GraphEdge
+from src.parsers.base import Entity, EntityType
+
+
+class TestGraphBuilder:
+    def setup_method(self):
+        self.builder = GraphBuilder(GraphType.DIRECTED)
+
+    def test_add_node(self):
+        node = GraphNode(
+            node_id="test_node",
+            node_type=NodeType.FILE,
+            name="test.py",
+            file_path=Path("/test/test.py"),
+        )
+        node_id = self.builder.add_node(node)
+        assert node_id == "test_node"
+        assert len(self.builder.nodes) == 1
+
+    def test_add_multiple_nodes(self):
+        node1 = GraphNode(node_id="node1", node_type=NodeType.FILE, name="file1.py")
+        node2 = GraphNode(node_id="node2", node_type=NodeType.FILE, name="file2.py")
+        self.builder.add_node(node1)
+        self.builder.add_node(node2)
+        assert len(self.builder.nodes) == 2
+
+    def test_add_edge(self):
+        source = GraphNode(node_id="source", node_type=NodeType.FILE, name="source.py")
+        target = GraphNode(node_id="target", node_type=NodeType.FILE, name="target.py")
+        self.builder.add_node(source)
+        self.builder.add_node(target)
+
+        edge = GraphEdge(source="source", target="target", edge_type="imports")
+        self.builder.add_edge(edge)
+        assert len(self.builder.edges) == 1
+
+    def test_get_graph(self):
+        graph = self.builder.get_graph()
+        assert graph is not None
+
+    def test_get_node_by_id(self):
+        node = GraphNode(node_id="test", node_type=NodeType.FILE, name="test.py")
+        self.builder.add_node(node)
+        retrieved = self.builder.get_node_by_id("test")
+        assert retrieved is not None
+        assert retrieved.name == "test.py"
+
+    def test_get_nodes_by_type(self):
+        file_node = GraphNode(node_id="file1", node_type=NodeType.FILE, name="file.py")
+        func_node = GraphNode(node_id="func1", node_type=NodeType.FUNCTION, name="func")
+        self.builder.add_node(file_node)
+        self.builder.add_node(func_node)
+
+        file_nodes = self.builder.get_nodes_by_type(NodeType.FILE)
+        func_nodes = self.builder.get_nodes_by_type(NodeType.FUNCTION)
+        assert len(file_nodes) == 1
+        assert len(func_nodes) == 1
+
+    def test_serialize(self):
+        node = GraphNode(
+            node_id="test",
+            node_type=NodeType.FILE,
+            name="test.py",
+            file_path=Path("/test.py"),
+            start_line=1,
+            end_line=10,
+        )
+        self.builder.add_node(node)
+
+        data = self.builder.serialize()
+        assert "nodes" in data
+        assert "edges" in data
+        assert len(data["nodes"]) == 1
+        assert data["nodes"][0]["name"] == "test.py"
+
+    def test_deserialize(self):
+        data = {
+            "nodes": [
+                {
+                    "id": "test",
+                    "type": "file",
+                    "name": "test.py",
+                    "file_path": "/test.py",
+                    "start_line": 1,
+                    "end_line": 10,
+                }
+            ],
+            "edges": [],
+        }
+        self.builder.deserialize(data)
+        assert len(self.builder.nodes) == 1
+
+    def test_get_subgraph(self):
+        node1 = GraphNode(node_id="n1", node_type=NodeType.FILE, name="f1.py")
+        node2 = GraphNode(node_id="n2", node_type=NodeType.FILE, name="f2.py")
+        node3 = GraphNode(node_id="n3", node_type=NodeType.FILE, name="f3.py")
+        self.builder.add_node(node1)
+        self.builder.add_node(node2)
+        self.builder.add_node(node3)
+
+        subgraph = self.builder.get_subgraph(["n1", "n2"])
+        assert subgraph.number_of_nodes() == 2
+
+
+class TestGraphNode:
+    def test_default_label(self):
+        node = GraphNode(node_id="test", node_type=NodeType.FILE, name="test.py")
+        assert node.label == "test.py"
+
+    def test_custom_label(self):
+        node = GraphNode(
+            node_id="test",
+            node_type=NodeType.FILE,
+            name="test.py",
+            label="Custom Label",
+        )
+        assert node.label == "Custom Label"
+
+    def test_default_style_and_shape(self):
+        node = GraphNode(node_id="test", node_type=NodeType.FILE, name="test.py")
+        assert node.style == "filled"
+        assert node.shape == "ellipse"
+
+
+class TestGraphEdge:
+    def test_default_edge_type(self):
+        edge = GraphEdge(source="a", target="b")
+        assert edge.edge_type == "depends"
+
+    def test_custom_edge_type(self):
+        edge = GraphEdge(source="a", target="b", edge_type="imports")
+        assert edge.edge_type == "imports"
+
+    def test_edge_with_label(self):
+        edge = GraphEdge(source="a", target="b", label="imports os")
+        assert edge.label == "imports os"