How can i mock the EventHubConsumerClient callback args with Jest - node.js

Question

I am creating an event hub consumer using the example code from https://learn.microsoft.com/en-us/azure/event-hubs/event-hubs-node-get-started-send
How should I mock the events and context which are passed a arguments to the callback?
const { EventHubConsumerClient, earliestEventPosition } = require("#azure/event-hubs");
const { ContainerClient } = require("#azure/storage-blob");
const { BlobCheckpointStore } = require("#azure/eventhubs-checkpointstore-blob");
const connectionString = "EVENT HUBS NAMESPACE CONNECTION STRING";
const eventHubName = "EVENT HUB NAME";
const consumerGroup = "$Default"; // name of the default consumer group
const storageConnectionString = "AZURE STORAGE CONNECTION STRING";
const containerName = "BLOB CONTAINER NAME";
async function main() {
// Create a blob container client and a blob checkpoint store using the client.
const containerClient = new ContainerClient(storageConnectionString, containerName);
const checkpointStore = new BlobCheckpointStore(containerClient);
// Create a consumer client for the event hub by specifying the checkpoint store.
const consumerClient = new EventHubConsumerClient(consumerGroup, connectionString, eventHubName, checkpointStore);
// Subscribe to the events, and specify handlers for processing the events and errors.
const subscription = consumerClient.subscribe({
processEvents: async (events, context) => {
if (events.length === 0) {
console.log(`No events received within wait time. Waiting for next interval`);
return;
}
for (const event of events) {
console.log(`Received event: '${event.body}' from partition: '${context.partitionId}' and consumer group: '${context.consumerGroup}'`);
}
// Update the checkpoint.
await context.updateCheckpoint(events[events.length - 1]);
},
processError: async (err, context) => {
console.log(`Error : ${err}`);
}
},
{ startPosition: earliestEventPosition }
);
// After 30 seconds, stop processing.
await new Promise((resolve) => {
setTimeout(async () => {
await subscription.close();
await consumerClient.close();
resolve();
}, 30000);
});
}
main().catch((err) => {
console.log("Error occurred: ", err);
});

Answer 1

I assume that you want to know about the types of these two? The processEvents callback has the following signature
type ProcessEventsHandler = (
events: ReceivedEventData[],
context: PartitionContext
) => Promise<void>
Here's the ref doc for ReceivedEventData: https://learn.microsoft.com/en-us/javascript/api/#azure/event-hubs/receivedeventdata?view=azure-node-latest
and ref doc for PartitionContext: https://learn.microsoft.com/en-us/javascript/api/#azure/event-hubs/partitioncontext?view=azure-node-latest
Not too familar with jest. Here's what I tried:
async function processEvents(events, context) {
if (events.length === 0) {
console.log(`No events received within wait time. Waiting for next interval`);
return;
}
for (const event of events) {
console.log(`Received event: '${event.body}' from partition: '${context.partitionId}' and consumer group: '${context.consumerGroup}'`);
}
// Update the checkpoint.
await context.updateCheckpoint(events[events.length - 1]);
}
test('empty events', async () => {
const context = {
updateCheckpoint: jest.fn()
};
await processEvents([], context);
expect(context.updateCheckpoint.mock.calls.length).toBe(0);
});
test('non-empty events', async () => {
const context = {
updateCheckpoint: jest.fn()
};
await processEvents([{ body: "hello"}], context);
console.dir(context.updateCheckpoint.mock);
expect(context.updateCheckpoint.mock.calls.length).toBe(1);
});