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)
debuggerPort	number	✅	override the port which the emulator will run the debug server on (default: auto)

Returns

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

Usage

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

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

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// Instantiate emulator and path to Cadence files

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beforeEach(async () => {

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

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await init(basePath)

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// Start emulator instance on auto-selected available ports

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await emulator.start()

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})

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})

emulator.stop()

Stops emulator instance. Returns Promise.

Arguments

This method does not expect any arguments.

Usage

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

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

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// Instantiate emulator and path to Cadence files

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beforeEach(async () => {

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

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await init(basePath)

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await emulator.start()

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})

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// Stop emulator, so it could be restarted

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afterEach(async () => {

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await emulator.stop()

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})

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})

emulator.setLogging(newState)

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

Arguments

Name	Type	Description
newState	boolean	Enable/disable logging

Usage

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

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

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// Instantiate emulator and path to Cadence files

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beforeEach(async () => {

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

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await init(basePath)

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await emulator.start()

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})

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// Stop emulator, so it could be restarted

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afterEach(async () => {

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await emulator.stop()

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})

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

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// Turn on logging from begining

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emulator.setLogging(true)

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// some asserts and interactions

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// Turn off logging for later calls

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emulator.setLogging(false)

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// more asserts and interactions here

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})

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})