print comamnd output in error case

build_server/__init__.py

@@ -2,15 +2,23 @@
 
 from os import environ
 from flask import Flask, request
-from subprocess import check_output
+from subprocess import check_output, CalledProcessError
 import json
+from sys import stderr
 
 app = Flask(__name__)
 
 @app.route('/<strategy>', methods=['POST'])
 def build(strategy):
-    return check_output([
-        f"/{environ['STRATEGIES_DIR']}/{strategy}",
-        json.dumps(request.get_json(), sort_keys=True, indent=4),
-        json.dumps(request.args.to_dict()),
-    ])
+    try:
+        return check_output([
+            f"{environ['STRATEGIES_DIR']}/{strategy}",
+            json.dumps(request.get_json(), sort_keys=True, indent=4),
+            json.dumps(request.args.to_dict()),
+        ])
+    except CalledProcessError as error:
+        print(error.stdout, file=stderr)
+        print(error.stderr, file=stderr)
+
+        raise error
+