Index: flang/test/Semantics/collectives01.f90
===================================================================
--- flang/test/Semantics/collectives01.f90
+++ flang/test/Semantics/collectives01.f90
@@ -1,46 +1,111 @@
 ! RUN: %python %S/test_errors.py %s %flang_fc1
 ! XFAIL: *
-! Check for semantic errors in co_sum() subroutine calls
-! To Do: add co_sum to the evaluation stage
+! This test checks for semantic errors in co_sum subroutine calls based on
+! the co_reduce interface defined in section 16.9.50 of the Fortran 2018 standard.
+! To Do: add co_sum to the list of intrinsics
 
-module test_co_sum
+program test_co_sum
   implicit none
 
-contains
+  integer i, status, integer_array(1), coindexed_integer[*]
+  complex c, complex_array(1,1,1, 1,1,1, 1,1,1, 1,1,1, 1,1,1) 
+  double precision d, double_precision_array(1)
+  real r, real_array(1), coindexed_real[*]
 
-  subroutine test
+  character(len=1) message, coindexed_character[*], character_array(1)
+  logical bool
   
-    integer i, status
-    real array(1)
-    complex z(1,1,1, 1,1,1, 1,1,1, 1,1,1, 1,1,1) 
-    character(len=1) message
+  !___ standard-conforming calls with no keyword arguments ___
+  call co_sum(i)
+  call co_sum(c)
+  call co_sum(d)
+  call co_sum(r)
+  call co_sum(i, 1)
+  call co_sum(c, 1, status)
+  call co_sum(d, 1, status, message)
+  call co_sum(r, 1, status, message)
+  call co_sum(integer_array)
+  call co_sum(complex_array, 1)
+  call co_sum(double_precision_array, 1, status)
+  call co_sum(real_array, 1, status, message)
+
+  !___ standard-conforming calls with keyword arguments ___
+
+  ! all arguments present
+  call co_sum(a=i, result_image=1, stat=status, errmsg=message) 
+
+  ! one optional argument not present
+  call co_sum(a=i,                 stat=status, errmsg=message) 
+  call co_sum(a=i, result_image=1,              errmsg=message)
+  call co_sum(a=i, result_image=1, stat=status                )
+
+  ! two optional arguments not present
+  call co_sum(a=i, result_image=1                             ) 
+  call co_sum(a=i,                 stat=status                )
+  call co_sum(a=i,                              errmsg=message) 
+
+  ! no optional arguments present
+  call co_sum(a=i                                             ) 
+
+  !___ non-standard-conforming calls ___
+
+  !ERROR: missing mandatory 'a=' argument
+  call co_sum(result_image=1, stat=status, errmsg=message)
+
+  ! argument 'a' shall be of numeric type
+  !ERROR: Actual argument for 'a=' has bad type 'LOGICAL(4)'
+  call co_sum(bool)
+  
+  ! argument 'a' is intent(inout)
+  !ERROR: Actual argument associated with INTENT(IN OUT) dummy argument 'a=' must be definable
+  call co_sum(a=1+1)
   
-    ! correct calls, should produce no errors
-    call co_sum(i)
-    call co_sum(i,   1)
-    call co_sum(i,   1,              status)
-    call co_sum(i,   1,              stat=status)
-    call co_sum(i,   1,                           errmsg=message)
-    call co_sum(i,   1,              stat=status, errmsg=message)
-    call co_sum(i,   result_image=1, stat=status, errmsg=message)
-    call co_sum(a=i, result_image=1, stat=status, errmsg=message)
-    call co_sum(i,   result_image=1, stat=status, errmsg=message)
+  ! argument 'a' shall not be a coindexed object
+  !ERROR: to be determined
+  call co_sum(a=coindexed_real[1])
   
-    call co_sum(array, result_image=1, stat=status, errmsg=message)
-    call co_sum(z, result_image=1, stat=status, errmsg=message)
+  ! 'result_image' argument shall be a integer
+  !ERROR: Actual argument for 'result_image=' has bad type 'LOGICAL(4)'
+  call co_sum(i, result_image=bool)
+  
+  ! 'result_image' argument shall be an integer scalar
+  !ERROR: 'result_image=' argument has unacceptable rank 1
+  call co_sum(c, result_image=integer_array)
+
+  ! argument 'stat' shall be intent(out)
+  !ERROR: Actual argument associated with INTENT(OUT) dummy argument 'stat=' must be definable
+  call co_sum(a=i, result_image=1, stat=1+1, errmsg=message)
+
+  ! 'stat' argument shall be noncoindexed
+  !ERROR: to be determined
+  call co_sum(d, stat=coindexed_integer[1])
+ 
+  ! 'stat' argument shall be an integer
+  !ERROR: Actual argument for 'stat=' has bad type 'CHARACTER(KIND=1,LEN=1_8)'
+  call co_sum(r, stat=message)
  
-    ! the error is seen as an incorrect type for the stat= argument
-    !ERROR: Actual argument for 'stat=' has bad type 'CHARACTER(KIND=1,LEN=1_8)'
-    call co_sum(i, 1, message)
+  ! 'stat' argument shall be an integer scalar
+  !ERROR: 'stat=' argument has unacceptable rank 1
+  call co_sum(i, stat=integer_array)
  
-    ! the error is seen as too many arguments to the co_sum() call
-    !ERROR: too many actual arguments for intrinsic 'co_sum'
-    call co_sum(i,   result_image=1, stat=status, errmsg=message, 3.4)
+  ! 'errmsg' argument shall be intent(inout)
+  !ERROR: Actual argument associated with INTENT(IN OUT) dummy argument 'errmsg=' must be definable
+  call co_sum(a=i, result_image=1, stat=status, errmsg='c')
   
-    ! keyword argument with incorrect type
-    !ERROR: unknown keyword argument to intrinsic 'co_sum'
-    call co_sum(fake=3.4)
+  ! 'errmsg' argument shall be noncoindexed
+  !ERROR: to be determined
+  call co_sum(c, errmsg=coindexed_character[1])
+ 
+  ! 'errmsg' argument shall be character scalar
+  !ERROR: 'errmsg=' argument has unacceptable rank 1
+  call co_sum(d, errmsg=character_array)
+ 
+  ! the error is seen as too many arguments to the co_sum() call
+  !ERROR: too many actual arguments for intrinsic 'co_sum'
+  call co_sum(r, result_image=1, stat=status, errmsg=message, 3.4)
   
-  end subroutine
-
-end module test_co_sum
+  ! keyword argument with incorrect name
+  !ERROR: unknown keyword argument to intrinsic 'co_sum'
+  call co_sum(fake=3.4)
+  
+end program test_co_sum