Tessel-Mocks

Allows local runtime for software designed for the Tessel 2.

Tessel 2 makes the require('tessel') package available once your code has been run on or pushed to the device. Unfortunately, the tessel package is not available locally, so when the script is run on your development machine the execution will halt with a missing package error.

This repo allows users to mock the functionality of the actual tessel device on a local machine.

Based loosely on https://github.com/samilamti/tessel-fakes

Usage

In your main script, near the rest of the require statements, replace the var tessel = require("tessel") with the following:

try {
    var tessel = require("tessel");
} catch(e) {
    console.error("Tessel not found - running mocks instead");
    var Tessel = require('tessel-mocks');
    tessel = new Tessel();
}

From this point on when running locally, the Tessel commands will print statements in the console instead of performing actions on the device.

• To run code on the Tessel: t2 run index.js
• To run code locally: node index.js

Example Comparison

When running on the Tessel, this code will flash LED3 (blue) every 2 seconds:

setInterval(function(){
  tessel.led[3].toggle();
}, 2000);

... but when running locally with node index.js, the console prints this:

Tessel not found - running mocks instead
TM | Toggled LED2 on
TM | Toggled LED2 off
TM | Toggled LED2 on

Mocking Responses

Serial communication devices can be mocked by passing additional parameters in any method that supports a callback. These extra parameters do not affect Tessel runtime and will be ignored on the device, but while running locally they will return the values specified.

To do this, pass 2 extra parameters (as if they were the callback values) to the target functions. Take the I2C Transfer method:

i2c.transfer(txbuf, rxlen, callback);

... and this becomes:

i2c.transfer(txbuf, rxlen, callback, mockError, mockReturn);

Example: BME280 I2C

This code prints no error and returns the ID of the BME280 device (which is 60):

var slaveAddress = 0x77;
var readLength = 1;
var i2c = new tessel.port.A.I2C(slaveAddress)
 
i2c.transfer(new Buffer([0xD0]), readLength, function (err, rx) {
  console.log('error returned by I2C Slave: ', err)
  console.log('buffer returned by I2C slave ('+slaveAddress.toString(16)+'):', rx);
});

Output:

INFO Running index.js...
error returned by I2C Slave:  null
buffer returned by I2C slave (77): <Buffer 60>

If this script is run locally with node index.js, the callback will not contain data:

INFO Running index.js...
Tessel not found - running mocks instead
TM | I2C Transfer: �
error returned by I2C Slave:  [Error]
buffer returned by I2C slave (77): undefined

Instead, if mock responses are passed in:

var slaveAddress = 0x77;
var readLength = 1;
var i2c = new tessel.port.A.I2C(slaveAddress)
 
i2c.transfer(new Buffer([0xD0]), readLength, function (err, rx) {
  console.log('error returned by I2C Slave: ', err)
  console.log('buffer returned by I2C slave ('+slaveAddress.toString(16)+'):', rx);
}, 'Test Error', '99');

... then the mock data will be populated in console:

Tessel not found - running mocks instead
TM | I2C Transfer: �
error returned by I2C Slave:  [Error: Test Error]
buffer returned by I2C slave (77): 99

Todo Mocks

• LEDs
• Digital Pins
• Analog Pins
• Interrupt Pins
• Ports
• UART
• SPI
• I2C
• PWM
• Button