How to mock ElasticSearch client specific method - node.js

Question

I have code in which I make a call to elasticsearch indices stats. Tried mocking it following way but did not work.
esIndicesStatsStub = sinon.stub(Client.indices.prototype, 'stats').returns({
promise: () => new Error()
})
The error I get is
TypeError: Cannot read property 'prototype' of undefined
I've source code like this
const { Client } = require('#elastic/elasticsearch')
const esClient = new Client({
node:'some https url'
})
esClient.indices.stats(params, function (err, data) {
if (err) {
reject(err);
} else {
if (data) {
//do something
}
//do some other thing
}
});
How do I mock elasticsearch properly with sinon? Because i'm not allowed to use #elastic/elasticsearch-mock

Answer 1

Since ES SDK defines some APIs such as indices via the getter function:
Object.defineProperties(API.prototype, {
//...
indices: {
get () { return this[kIndices] === null ? (this[kIndices] = new IndicesApi(this.transport)) : this[kIndices] }
},
//...
})
see v8.5.0/src/api/index.ts#L372
We should use stub.get(getterFn) API to replace a new getter for this stub.
For these APIs such as .bulk, .clearScroll which are assigned directly to API.prototype, you can call sinon.stub(Client.prototype, 'bulk') to stub them.
At last, since your code is defined in the module scope, the code will be executed when you import/require it. We should arrange our stubs first, then import/require the module. As you can see, I use dynamic import().
E.g.
index.ts:
import { Client } from '#elastic/elasticsearch';
const esClient = new Client({ node: 'http://localhost:9200' });
esClient.indices.stats({ index: 'a' }).then(console.log);
index.test.ts:
import sinon from 'sinon';
import { Client } from '#elastic/elasticsearch';
import { IndicesStatsResponse } from '#elastic/elasticsearch/lib/api/types';
describe('74949441', () => {
it('should pass', async () => {
const indicesStatsResponseStub: IndicesStatsResponse = {
_shards: {
failed: 0,
successful: 1,
total: 2,
},
_all: {
uuid: '1',
},
};
const indicesApiStub = {
stats: sinon.stub().resolves(indicesStatsResponseStub),
};
sinon.stub(Client.prototype, 'indices').get(() => indicesApiStub);
await import('./');
sinon.assert.calledWithExactly(indicesApiStub.stats, { index: 'a' });
});
});
Test result:
74949441
{
_shards: { failed: 0, successful: 1, total: 2 },
_all: { uuid: '1' }
}
✓ should pass (609ms)
1 passing (614ms)
----------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files | 100 | 100 | 100 | 100 |
index.ts | 100 | 100 | 100 | 100 |
----------|---------|----------|---------|---------|-------------------
package versions:
"#elastic/elasticsearch": "^8.5.0",
"sinon": "^8.1.1",
"mocha": "^8.2.1",