Merge pull request #2607 from stan-dev/add_lchoose_exception

Ignore lchoose in expression tests

Author: rok-cesnovar

test/sig_utils.py

@@ -138,6 +138,7 @@ def get_cpp_type(stan_type):
 # list of functions we do not test. These are mainly functions implemented in compiler
 # (not in Stan Math).
 ignored = [
+    "lchoose",
     "lmultiply",
     "assign_add",
     "assign_divide",