Add error_trace to string representation of an Error

If the `error_trace` payload is available, add it to the string
representation of the Error class.

CHANGES.txt

@@ -10,6 +10,8 @@ Unreleased
   about necessary migration steps.
 - Configured DB API interface attribute ``threadsafety = 1``, which signals
   "Threads may share the module, but not connections."
+- Added ``error_trace`` to string representation of an Error to relay
+  server stacktraces into exception messages.
 
 .. _Migrate from crate.client to sqlalchemy-cratedb: https://cratedb.com/docs/sqlalchemy-cratedb/migrate-from-crate-client.html
 .. _sqlalchemy-cratedb: https://pypi.org/project/sqlalchemy-cratedb/

src/crate/client/exceptions.py

@@ -30,6 +30,11 @@ def __init__(self, msg=None, error_trace=None):
         super(Error, self).__init__(msg)
         self.error_trace = error_trace
 
+    def __str__(self):
+        if self.error_trace is None:
+            return super().__str__()
+        return "\n".join([super().__str__(), str(self.error_trace)])
+
 
 class Warning(Exception):
     pass

src/crate/client/test_exceptions.py

@@ -0,0 +1,14 @@
+import unittest
+
+from crate.client import Error
+
+
+class ErrorTestCase(unittest.TestCase):
+
+    def test_error_with_msg(self):
+        err = Error("foo")
+        self.assertEqual(str(err), "foo")
+
+    def test_error_with_error_trace(self):
+        err = Error("foo", error_trace="### TRACE ###")
+        self.assertEqual(str(err), "foo\n### TRACE ###")