context-succeed-fail-done.md

Verifying context.succeed(), context.fail and context.done()

Verifying context.succeed()

When the Lambda calls context.succeed(), verification can be performed using expectSucceed(). If the code calls anything else other than context.succeed() or context.done( null, result ), then the test will fail.

const LambdaTester = require( 'lambda-tester' );

const myHandler = require( '../my-handler' ).handler;

describe( 'handler', function() {

	it( 'test success', function() {

		return LambdaTester( myHandler )
			.event( { name: 'Fred' } )
			.expectSucceed();
	});
});

To verify the state of the result, the test can include a validator to inspect the result:

const LambdaTester = require( 'lambda-tester' );

// Mocha using Chai
const expect = require( 'chai' ).expect;

const myHandler = require( '../my-handler' ).handler;

describe( 'handler', function() {

	it( 'test success', function() {

		return LambdaTester( myHandler )
			.event( { name: 'Fred' } )
			.expectSucceed( ( result ) => {

				expect( result.userId ).to.exist;
				expect( result.user ).to.equal( 'fredsmith' );
			});
	});
});

Note: context.succeed() cannot be used to verify callback( null, result ).

Verifying context.fail()

As with verifying success, when the Lambda calls context.fail(), verification can be performed using expectFail(). If the code calls anything else other than context.fail() or context.done( err ), then the test will fail.

const LambdaTester = require( 'lambda-tester' );

const myHandler = require( '../index' ).handler;

describe( 'handler', function() {

	it( 'test failure', function() {

		return LambdaTester( myHandler )
			.event( { name: 'Unknown' } )
			.expectFail();
	});
});

To verify the state of the error, the test can include a validator to inspect the error:

const LambdaTester = require( 'lambda-tester' );

// Mocha using Chai
const expect = require( 'chai' ).expect;

const myHandler = require( '../index' ).handler;

describe( 'handler', function() {

	it( 'test failure', function() {

		return LambdaTester( myHandler )
			.event( { name: 'Unknown' } )
			.expectFail( ( err ) => {

				expect( err.message ).to.equal( 'User not found' );
			});
	});
});

Note: context.fail() cannot be used to verify callback( err ).

Verifying context.done()

Internally, AWS Lambda routes context.done() to context.succed() and context.fail() for results or errors respectively, thus you can use the methods described above to verify those scenarios.