feat: add fork choice endpoint to api spec tests

tests/api/endpoints/test_fork_choice.py

@@ -0,0 +1,116 @@
+"""Tests for the fork choice endpoint."""
+
+import httpx
+
+
+def get_fork_choice(server_url: str) -> httpx.Response:
+    """Fetch fork choice tree from the server."""
+    return httpx.get(
+        f"{server_url}/lean/v0/fork_choice",
+        headers={"Accept": "application/json"},
+    )
+
+
+class TestForkChoice:
+    """Tests for the /lean/v0/fork_choice endpoint."""
+
+    def test_returns_200(self, server_url: str) -> None:
+        """Fork choice endpoint returns 200 status code."""
+        response = get_fork_choice(server_url)
+        assert response.status_code == 200
+
+    def test_content_type_is_json(self, server_url: str) -> None:
+        """Fork choice endpoint returns JSON content type."""
+        response = get_fork_choice(server_url)
+        content_type = response.headers.get("content-type", "")
+        assert "application/json" in content_type
+
+    def test_has_nodes(self, server_url: str) -> None:
+        """Fork choice response has a nodes array."""
+        data = get_fork_choice(server_url).json()
+
+        assert "nodes" in data
+        assert isinstance(data["nodes"], list)
+        assert len(data["nodes"]) > 0
+
+    def test_node_structure(self, server_url: str) -> None:
+        """Each node has root, slot, parent_root, proposer_index, and weight."""
+        data = get_fork_choice(server_url).json()
+        node = data["nodes"][0]
+
+        assert isinstance(node["root"], str)
+        assert node["root"].startswith("0x")
+        assert len(node["root"]) == 66
+
+        assert isinstance(node["slot"], int)
+        assert node["slot"] >= 0
+
+        assert isinstance(node["parent_root"], str)
+        assert node["parent_root"].startswith("0x")
+        assert len(node["parent_root"]) == 66
+
+        assert isinstance(node["proposer_index"], int)
+        assert node["proposer_index"] >= 0
+
+        assert isinstance(node["weight"], int)
+        assert node["weight"] >= 0
+
+    def test_has_head(self, server_url: str) -> None:
+        """Fork choice response has a valid head root."""
+        data = get_fork_choice(server_url).json()
+
+        assert "head" in data
+        assert isinstance(data["head"], str)
+        assert data["head"].startswith("0x")
+        assert len(data["head"]) == 66
+
+    def test_has_justified_checkpoint(self, server_url: str) -> None:
+        """Fork choice response has a justified checkpoint with slot and root."""
+        data = get_fork_choice(server_url).json()
+
+        assert "justified" in data
+        justified = data["justified"]
+
+        assert isinstance(justified["slot"], int)
+        assert justified["slot"] >= 0
+
+        assert isinstance(justified["root"], str)
+        assert justified["root"].startswith("0x")
+        assert len(justified["root"]) == 66
+
+    def test_has_finalized_checkpoint(self, server_url: str) -> None:
+        """Fork choice response has a finalized checkpoint with slot and root."""
+        data = get_fork_choice(server_url).json()
+
+        assert "finalized" in data
+        finalized = data["finalized"]
+
+        assert isinstance(finalized["slot"], int)
+        assert finalized["slot"] >= 0
+
+        assert isinstance(finalized["root"], str)
+        assert finalized["root"].startswith("0x")
+        assert len(finalized["root"]) == 66
+
+    def test_has_safe_target(self, server_url: str) -> None:
+        """Fork choice response has a valid safe_target root."""
+        data = get_fork_choice(server_url).json()
+
+        assert "safe_target" in data
+        assert isinstance(data["safe_target"], str)
+        assert data["safe_target"].startswith("0x")
+        assert len(data["safe_target"]) == 66
+
+    def test_has_validator_count(self, server_url: str) -> None:
+        """Fork choice response has a non-negative validator count."""
+        data = get_fork_choice(server_url).json()
+
+        assert "validator_count" in data
+        assert isinstance(data["validator_count"], int)
+        assert data["validator_count"] >= 0
+
+    def test_head_is_in_nodes(self, server_url: str) -> None:
+        """The head root appears in the nodes list."""
+        data = get_fork_choice(server_url).json()
+        node_roots = {node["root"] for node in data["nodes"]}
+        assert data["head"] in node_roots