fix(reduce): fail if empty, if one return the element

rethinkdb_mock/ast.py

@@ -8,6 +8,7 @@
 from future.utils import iteritems
 from future.utils import text_type
 from past.utils import old_div
+from rethinkdb.errors import ReqlNonExistenceError
 
 from rethinkdb_mock import ast_base
 from rethinkdb_mock import joins
@@ -256,6 +257,12 @@ class Or(BinOp):
 
 class Reduce(ByFuncBase):
  def do_run(self, sequence, reduce_fn, arg, scope):
+ if len(sequence) == 0:
+ raise ReqlNonExistenceError("Cannot reduce over an empty stream")
+
+ if len(sequence) == 1:
+ return sequence[0]
+
  first, second = sequence[0:2]
  result = reduce_fn([first, second])
  for elem in sequence[2:]:

tests/functional/test_misc.py

@@ -1,4 +1,5 @@
 from rethinkdb import r
+from rethinkdb.errors import ReqlNonExistenceError
 from rethinkdb.errors import RqlRuntimeError
 from tests.common import as_db_and_table
 from tests.common import assertEqual
@@ -399,6 +400,32 @@ def test_reduce_1(self, conn):
  )
  assertEqual(expected, result)
 
+ def test_reduce_one(self, conn):
+ expected = {"count": 1}
+ result = (
+ r.expr([{"count": 1}])
+ .reduce(
+ lambda left, right: {
+ "count": left["count"] + right["count"],
+ }
+ )
+ .run(conn)
+ )
+ assertEqual(expected, result)
+
+ def test_reduce_errors(self, conn):
+ err = None
+ try:
+ r.expr([]).reduce(
+ lambda left, right: {
+ "count": left["count"] + right["count"],
+ }
+ ).run(conn)
+ except ReqlNonExistenceError as e:
+ err = e
+
+ assert isinstance(err, ReqlNonExistenceError)
+
 
 class TestBranch(MockTest):
  @staticmethod