Fix duplicate reject reason value for ConditionallyRequiredFieldMissing

Per FIX spec (tag 373/380), the value is 8, not 5. Adds a regression
test guarding the two reject reasons against future collision.

Fixes #721.

Author: vsaraikin

errors.go

@@ -31,7 +31,7 @@ const (
 	rejectReasonUnsupportedMessageType                    = 3
 	rejectReasonTagSpecifiedWithoutAValue                 = 4
 	rejectReasonValueIsIncorrect                          = 5
-	rejectReasonConditionallyRequiredFieldMissing         = 5
+	rejectReasonConditionallyRequiredFieldMissing         = 8
 	rejectReasonIncorrectDataFormatForValue               = 6
 	rejectReasonCompIDProblem                             = 9
 	rejectReasonSendingTimeAccuracyProblem                = 10

errors_test.go

@@ -141,7 +141,9 @@ func TestValueIsIncorrect(t *testing.T) {
 
 func TestConditionallyRequiredFieldMissing(t *testing.T) {
 	var (
-		expectedRejectReason         = 5
+		// Per FIX spec (tag 373/380 enum), ConditionallyRequiredFieldMissing
+		// is value 8, distinct from ValueIsIncorrect (value 5). See issue #721.
+		expectedRejectReason         = 8
 		expectedRefTagID         Tag = 44
 		expectedErrorString          = fmt.Sprintf("Conditionally Required Field Missing (%d)", expectedRefTagID)
 		expectedIsBusinessReject     = true
@@ -159,6 +161,10 @@ func TestConditionallyRequiredFieldMissing(t *testing.T) {
 	if msgRej.IsBusinessReject() != expectedIsBusinessReject {
 		t.Error("Expected IsBusinessReject to be true\n")
 	}
+	// Regression guard: the two reject reasons must not collide.
+	if msgRej.RejectReason() == ValueIsIncorrect(expectedRefTagID).RejectReason() {
+		t.Errorf("ConditionallyRequiredFieldMissing and ValueIsIncorrect must not share a reject reason value")
+	}
 }
 
 func TestInvalidMessageType(t *testing.T) {