Emulator

Flow Javascript Testing Framework exposes emulator singleton allowing you to run and stop emulator instance programmatically. There are two methods available on it.

emulator.start(options)

Starts emulator on random available port, unless overriden in options. Returns Promise.

Arguments

Name	Type	Optional	Description
options	EmulatorOptions	✅	an object containing options for starting the emulator

EmulatorOptions

Key	Type	Optional	Description
logging	boolean	✅	whether log messages from emulator shall be added to the output (default: false)
flags	string	✅	custom command-line flags to supply to the emulator (default: "")
adminPort	number	✅	override the port which the emulator will run the admin server on (default: auto)
restPort	number	✅	override the port which the emulator will run the REST server on (default: auto)
grpcPort	number	✅	override the port which the emulator will run the GRPC server on (default: auto)

Returns

Type	Description
Promise	Promise, which resolves to true if emulator started successfully

Usage

_13

import {emulator, init} from "@onflow/flow-js-testing"

_13

_13

describe("test setup", () => {

_13

// Instantiate emulator and path to Cadence files

_13

beforeEach(async () => {

_13

const basePath = path.resolve(__dirname, "../cadence")

_13

_13

await init(basePath)

_13

_13

// Start emulator instance on auto-selected available ports

_13

await emulator.start()

_13

})

_13

})

emulator.stop()

Stops emulator instance. Returns Promise.

Arguments

This method does not expect any arguments.

Usage

_16

import {emulator, init} from "@onflow/flow-js-testing"

_16

_16

describe("test setup", () => {

_16

// Instantiate emulator and path to Cadence files

_16

beforeEach(async () => {

_16

const basePath = path.resolve(__dirname, "../cadence")

_16

_16

await init(basePath)

_16

await emulator.start()

_16

})

_16

_16

// Stop emulator, so it could be restarted

_16

afterEach(async () => {

_16

await emulator.stop()

_16

})

_16

})

emulator.setLogging(newState)

Set logging flag on emulator, allowing to temporally enable/disable logging.

Arguments

Name	Type	Description
newState	boolean	Enable/disable logging

Usage

_26

import {emulator, init} from "@onflow/flow-js-testing"

_26

_26

describe("test setup", () => {

_26

// Instantiate emulator and path to Cadence files

_26

beforeEach(async () => {

_26

const basePath = path.resolve(__dirname, "../cadence")

_26

_26

await init(basePath)

_26

await emulator.start()

_26

})

_26

_26

// Stop emulator, so it could be restarted

_26

afterEach(async () => {

_26

await emulator.stop()

_26

})

_26

_26

test("basic test", async () => {

_26

// Turn on logging from begining

_26

emulator.setLogging(true)

_26

// some asserts and interactions

_26

_26

// Turn off logging for later calls

_26

emulator.setLogging(false)

_26

// more asserts and interactions here

_26

})

_26

})