Update tests for changed function node low-level output

Fixes #4683

packages/node_modules/@node-red/nodes/core/function/10-function.js

@@ -438,10 +438,9 @@ module.exports = function(RED) {
 
                             //store the error in msg to be used in flows
                             msg.error = err;
-
-                            var line = 0;
-                            var errorMessage;
                             if (stack.length > 0) {
+                                let line = 0;
+                                let errorMessage;
                                 while (line < stack.length && stack[line].indexOf("ReferenceError") !== 0) {
                                     line++;
                                 }
@@ -455,11 +454,13 @@ module.exports = function(RED) {
                                         errorMessage += " (line "+lineno+", col "+cha+")";
                                     }
                                 }
+                                if (errorMessage) {
+                                    err.message = errorMessage
+                                }
                             }
-                            if (!errorMessage) {
-                                errorMessage = err.toString();
-                            }
-                            done(errorMessage);
+                            // Pass the whole error object so any additional properties
+                            // (such as cause) are preserved
+                            done(err);
                         }
                         else if (typeof err === "string") {
                             done(err);

packages/node_modules/@node-red/runtime/lib/flows/Flow.js

@@ -678,6 +678,9 @@ class Flow {
                 if (logMessage.hasOwnProperty('stack')) {
                     errorMessage.error.stack = logMessage.stack;
                 }
+                if (logMessage.hasOwnProperty('cause')) {
+                    errorMessage.error.cause = logMessage.cause;
+                }
                 targetCatchNode.receive(errorMessage);
                 handled = true;
             });

test/nodes/core/function/10-function_spec.js

@@ -390,7 +390,8 @@ describe('function node', function() {
                     msg.should.have.property('level', helper.log().ERROR);
                     msg.should.have.property('id', 'n1');
                     msg.should.have.property('type', 'function');
-                    msg.should.have.property('msg', 'ReferenceError: retunr is not defined (line 2, col 1)');
+                    msg.should.have.property('msg')
+                    msg.msg.message.should.equal('ReferenceError: retunr is not defined (line 2, col 1)');
                     done();
                 } catch(err) {
                     done(err);
@@ -659,7 +660,8 @@ describe('function node', function() {
                 msg.should.have.property('level', helper.log().ERROR);
                 msg.should.have.property('id', name);
                 msg.should.have.property('type', 'function');
-                msg.should.have.property('msg', 'Error: Callback must be a function');
+                msg.should.have.property('msg')
+                msg.msg.message.should.equal('Callback must be a function');
                 done();
             }
             catch (e) {