Added native test for Rf_isNull.

com.oracle.truffle.r.test.native/packages/testrffi/testrffi/R/testrffi.R

@@ -191,4 +191,8 @@ rffi.createNativeConnection <- function() {
 
 rffi.parseVector <- function(x) {
     .Call('test_ParseVector', x);
+}
+
+rffi.isNull <- function(x) {
+    .Call('test_isNull', x);
 }
\ No newline at end of file

com.oracle.truffle.r.test.native/packages/testrffi/testrffi/src/testrffi.c

@@ -533,3 +533,7 @@ SEXP test_ParseVector(SEXP src) {
     UNPROTECT(2);
     return result;
 }
+
+Rboolean test_isNull(SEXP x) {
+	return Rf_isNull(x);
+}

com.oracle.truffle.r.test.native/packages/testrffi/testrffi/src/testrffi.h

@@ -105,3 +105,5 @@ extern SEXP test_readConnection(SEXP conn);
 extern SEXP test_createNativeConnection(void);
 
 extern SEXP test_ParseVector(SEXP src);
+
+extern Rboolean test_isNUll(SEXP x);

com.oracle.truffle.r.test.native/packages/testrffi/testrffi/tests/simpleTests.R

@@ -86,6 +86,11 @@ rffi.parseVector('1+')
 for(i in seq(5000)) {
     rffi.preserve_object()
 }
+
 for(i in seq(5000)) {
     rffi.release_object()
-}
\ No newline at end of file
+}
+
+# test isNull
+rffi.isNull(NULL)
+