Cache YAML payloads in tests

Closes #39 (closed)

Pytest execution went from 221.70s on master to 30.20s on this branch.

tests/conftest.py

 # -*- coding: utf-8 -*-
+import hashlib
 import json
 import os
 import sys
 from pathlib import Path
 
 import pytest
+import yaml
 
 from arkindex.mock import MockApiClient
 from arkindex_worker.git import GitHelper, GitlabHelper
@@ -12,9 +14,37 @@ from arkindex_worker.worker import ElementsWorker
 
 FIXTURES_DIR = Path(__file__).resolve().parent / "data"
 
+__yaml_cache = {}
+
+
+@pytest.fixture
+def cache_yaml(monkeypatch):
+    """
+    Cache all calls to yaml.safe_load in order to speedup
+    every test cases that load the OpenAPI schema
+    """
+    # Keep a reference towards the original function
+    _original_yaml_load = yaml.safe_load
+
+    def _cached_yaml_load(yaml_payload):
+        # Create a unique cache key for direct YAML strings
+        # and file descriptors
+        if isinstance(yaml_payload, str):
+            key = hashlib.md5(yaml_payload.encode("utf-8")).hexdigest()
+        else:
+            key = yaml_payload.name
+
+        # Cache result
+        if key not in __yaml_cache:
+            __yaml_cache[key] = _original_yaml_load(yaml_payload)
+
+        return __yaml_cache[key]
+
+    monkeypatch.setattr(yaml, "safe_load", _cached_yaml_load)
+
 
 @pytest.fixture(autouse=True)
-def setup_api(responses, monkeypatch):
+def setup_api(responses, monkeypatch, cache_yaml):
 
     # Always use the environment variable first
     schema_url = os.environ.get("ARKINDEX_API_SCHEMA_URL")