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Node.js assert tracker.calls() Function

Last Updated : 14 May, 2022
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The tracker.calls() method is used to keep track of the number of times a function is executed. It returns a wrapper function that should be invoked at exact times. When tracker.verify() is executed, if the method has not been called precisely exact times, tracker.verify() will throw an exception.

Syntax:

tracker.calls([fn][, exact])

Parameters:

  • fn: The function to be monitored. A no-op function is the default value.
  • exact (number): The number of times. Its default value is 1.

Return Value: A wrapper function that wraps fn.

Example 1:

JavaScript 
import assert from 'node:assert';

const tracker = new assert.CallTracker();

function func() { console.log("Hello World") };

const callsfunc = tracker.calls(func, 2);

callsfunc();
callsfunc();

process.on('exit', () => {
    tracker.verify()
});

Output:

Hello World
Hello World

Example 2:

JavaScript 
import assert from 'node:assert';

const tracker = new assert.CallTracker();

function func() { console.log("Hello World") };

const callsfunc = tracker.calls(func, 2);

callsfunc();

process.on('exit', () => {
    tracker.verify()
});

Output:

 

Reference: https://nodejs.org/api/assert.html#trackercallsfn-exact


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Node.js assert.fail() Function

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