Should promises be implemented in the test helper, so node developers are free to choose callback-based or ES2017 async/await syntax?
I was a little annoyed that the test helper is callback-based, specially considering it has one method that returns a promise. I tried making a version that calls callbacks, but also returns a promise. And it works really well for me, it solves several problems:
- No increasing indentation for each call to an async function
- No worries about forgetting to catch an error in a callback
- More linear execution of code (the line that sends a message is now above the line that receives it)
Example:
it('should make payload lower case',function(done) {
var flow = [
{id:"n1",type:"lower-case",name:"test name",wires:[["n2"]]},
{id:"n2",type:"helper"}
];
helper.load(lowerNode,flow,function() {
var n2 = helper.getNode("n2");
var n1 = helper.getNode("n1");
n2.on("input",function(msg) {
try {
msg.should.have.property('payload','uppercase');
done();
} catch (e) {
done(e);
}
});
n1.receive({payload:"UpperCase"});
});
});
is now
it('should make payload lower case',async function() {
var flow = [
{id:"n1",type:"lower-case",name:"test name",wires:[["n2"]]},
{id:"n2",type:"helper"}
];
await helper.load(lowerNode,flow);
var n2 = helper.getNode("n2");
var n1 = helper.getNode("n1");
n1.receive({payload:"UpperCase"});
let msg = await n2.next("input");
msg.should.have.property('payload','uppercase');
});
You can try my version by changing your devDependency in package.json to:
"node-red-node-test-helper": "github:myplacedk/node-red-node-test-helper#async",
(and of course npm install)
I didn't document it yet, but I just made every method that takes a callback also return a promise. And I added a "next"-method that can be used as an alternative to "on". Events are queued, so you can process them linearly. If an event isn't in queue, "next" will wait until there's an event. If the event is "input", you'll get a clone of the message, just in case the message is changed during the flow.
Source: https://github.com/myplacedk/node-red-node-test-helper/tree/async
Changes in index.js: https://github.com/node-red/node-red-node-test-helper/compare/master...myplacedk:async?expand=1#diff-168726dbe96b3ce427e7fedce31bb0bc
Matching unit-test: https://github.com/node-red/node-red-node-test-helper/compare/master...myplacedk:async?expand=1#diff-fa77609e9ad7e21848f3e1b660d1ee26
