Introduction to testing

with Jest

ToC

  • What is testing?
  • Why we test software?
  • How we should procede?
  • What do we test on unit testing?

What is testing

What is testing

  • is an empirical
  • technical
  • investigation
  • conducted to provide stakeholders
  • with information
  • about the quality
  • of the product or service under test

Cem Kaner J.D., Ph.D., is a Professor of Software Engineering at Florida Institute of Technology

What is testing

  • is an empirical
  • technical
  • investigation
  • conducted to provide stakeholders
  • with information
  • about the quality
  • of the product or service under test

Cem Kaner J.D., Ph.D., is a Professor of Software Engineering at Florida Institute of Technology

Stakeholders

A stakeholder is any individual, group or organization that can affect, be affected by, or perceive itself to be affected [by a programme]

Quality

Software Quality

An important question in the testing process is "when should we stop?".

  • The answer is when system reliability is acceptable
  • or when the gain in reliability cannot compensate for the testing cost.

To answer either of these concerns we need a measurement of the quality of the system.

Bugs/LoC

Risk Driven Testing

Bugs fixed / found

Code Smells

Vulnerabilites

Regression errors

UX detriment

Deprecated dependencies

Acceptance incompleteness

What is testing

  • The process of [...]
  • evaluating a system or system component
  • [...] to verify that it satisfies specified requirements
  • or to identify differences between expected and actual results

(ANSI/IEEE Standard 729, 1983).

Main principles

Isolation: pure (no side effects) and controlled context

  • Too much isolation: mocking++ is also bad.
  • Too much isolation reduces the bug catchs.

 

Confidence:

  • Our test suite must enable confidence.

  • Our architecture must be testable.

  • Our logic models might be rethinked (private class fields)

Why testing

Why testing

Eric Elliot. Book and libraries author

Procedures (the How)

(while testing front end or backend applications)

(just one opinion)

Process Definition Proposition

⚡️⚡️ Waterfall

Process Definition Proposition

  1. Sprint grooming + planning
    1. Acceptance/​Requirements definition
    2. High Level Design (and documentation)
    3. ​Diagrams definition
  2. Detailed design
    1. TDD? Test design, tests implementation
  3. Code implementation
  4. Unit tests pass
  5. Integration/functional pass
  6. Acceptance/E2E pass
  7. Deploy/Deliver
  8. Document more
  9. Measure and gather feedback
  10. Repeat process

Different levels of testing

Testing pyramid... 😅

Unit

Integration

E2E

Static analysis: Eslint or static

type checking

Functional

Integration

E2E

Static analysis: Eslint or static

type checking

Unit

Usability

CB Compatibility

Regression

Security

Acceptance

Network

Visual

Soak

Smoke

Load

...it depends

Unit

Integration

E2E

Static analysis: Eslint or static

type checking

Jest

What is UNIT testing

What is UNIT testing

  • Automated tests
  • written and run by software developers
  • to ensure that a section of an application (known as the "unit")
  • meets its design and behaves as intended.

Hamill, Paul (2004). Unit Test Frameworks: Tools for High-Quality Software Development.

Unit testing should be...

Unit tests should focus on behaviors that are mostly pure:

  • Given the same inputs, always return the same output

  • Have no side-effects

All tests must be isolated from other tests. Tests should have no shared mutable state.

What to test on unit tests, then?

  • Local state modifications (most of the times you don't need to test the defaults)
  • Methods inputs and outputs
  • "Events" with expected structure
  • Calls to external services, but just the "contracts": API calls, global state calls...

Jest framework

  • Almost 0 config 🤷🏾‍♀️
  • Snapshot testing 📸
  • Isolated ‼️
  • Fast 🔥
  • Coverage 👀
  • Easy API 🙏🏾

Delightful JavaScript Testing Framework with a focus on simplicity.

Example

// import...

// import mocks or setup factory functions

describe('Title of test suite', () => {


    it('Title of test', () => {
        // ...
        // unit test content
        // ...
    })


})

Example

// import...

// import mocks or setup factory functions

describe('Title of test suite', () => {

    beforeAll(() => {
        console.log('starts this test suite')
    })

    it('Title of test', () => {
        // ...
        // unit test content
        // ...
    })

})

Example

// import...

// import mocks or setup factory functions

describe('Title of test suite', () => {

    beforeAll(() => {
        console.log('starts this test suite')
    })

    it('Title of test', () => {
        // ...
        // unit test content
        // ...
    })

    afterAll(() => {
        console.log('starts this test suite')
    })

})

Example

// import...


describe('Title of test suite', () => {

    it('Title of test', () => {
        // (optional) test phases

        // setup

        // act

        // assert

    })
})

DEMO

time

😮

Resources

Introduction to testing with Jest

By Paul Melero

Introduction to testing with Jest

What is unit testing and why should we test? What kind of things should we test on the unit tests?

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