ES3-2020-07 Testing techniques

07 Testing - Techniques
Enginyeria del Software 3
1
@drpicox — 2020

Summary
• Levels of Testing

• FIRST properties

• AAA structure

• Code Coverage

• Regression Tests

• Test doubles
2

Summary

• AAA structure

• Code Coverage


• Test doubles
3

Levels of Testing
• Acceptance Tests

• Programmers Tests
4

Acceptance Tests
• Readable by Stakeholders

• Natural language

• Aligned to Requirements

• High level

• Integrate many levels in the test

• Slow
5

Programmers Tests
• Fast to run

• Quick to code

• Fine grained

• Close to Requirements (Business rules)
6

Summary

• AAA structure

• Code Coverage


• Test doubles
8

FIRST properties
• Fast

• Isolates

• Repeatable

• Self-validating

• Timely
9

Fast
• Many hundreds or thousands per second

• Avoid slow logic

• Data bases

• External services

• Intensive computations

• ...
10

Isolates
• Failure reasons become obvious

• Each test runs individually

• No assumed initial state

• Not require other test run ﬁrst

• Can run alone

• Can run in random order

• new , new , new

• ...
11

Repeatable
• Run repeatedly in any order, any time

• No side eﬀects

• No globals/statics

• No time

• No random

• No databases

• No services

• No split test logic

• ...
12

Self-validating
• No manual evaluation required

• Only two outcomes

• Red/Green

• Fail/Pass
13

Timely
• Written before the code

• If you write test after code:

• You do not follow TDD

• You are not sure that the test works

• You forget test behaviours

• Your tests become useless

• You feel cheeting

• ...
14

Example
const notebook = new Notebook()
test("add a contact", () => {
notebook.add("John", 1234)
expect(notebook.get("John")).toBe(1234)
})
test("update contact", () => {
notebook.update("John", 3456)
})
test("remove a contact", () => {
notebook.remove("John")
expect(notebook.get("John")).toBeNull()
})
15

Example
test("add a contact", () => {
})
})
test("remove a contact", () => {
notebook.remove("John")
expect(notebook.get("John")).toBeNull()
})
16

Example
// Date changes each time
new Date();
// Result changes each call
Random.next();
// We are accessing a static/global
Notebook.add("John", 1234);
// Global + It is not self-validated
if (notebook.get("John") === 1234)
System.out.println("Sucess")
17

Summary


• AAA structure
• Code Coverage


• Test doubles
18

AAA Structure
• Arrange

• Prepare the initial states

• Call news and required sets before act

• Act

• Execute the actions required by the test

• Assert

• Gather results

• Expect the result values
19

AAA Structure
• Order is always kept

• Steps are not mixed

• Expect always simple results
20

Example
test("manage contacts", () => {
const notebook = new Notebook() // Arrange
notebook.add("John", 1234) // Act
expect(notebook.get("John")).toBe(1234) // Assert
notebook.update("John", 3456) // Act
expect(notebook.get("John")).toBe(3456) // Assert
notebook.delete("John") // Act
expect(notebook.get("John")).toBeNull() // Assert
})
21

Example
test("add contact", () => {
// Arrange
// Act
// Assert
})
// Arrange
// Act
// Assert
})
...
22

Summary


• AAA structure

• Code Coverage

• Test doubles
23

Code Coverage
24
Code Tested
Code Existing
%

Exemple
})
class Notebook {
add(name, phone) {
if (map.contains(name))
throw new Error(`Cannot add twice ${name}`)
map.put(name, phone)
}
}
25
Code Coverage: 66%
Uncovered line

Exemple
})
test('cannot add a duplicated contact', () => {
expect(() => notebook.add('John', 1111)).toThrow()
})
class Notebook {
add(name, phone) {
if (map.contains(name))
throw new Error(`Cannot add twice ${name}`)
}
}
26
Code Coverage: 100%

Exemple
})
class Notebook {
add(name, phone) {
}
}
27
Code Coverage: 100%

Número de tests
• 1 test base

• 1 test per condition

• &&, ||, if, while, for, ...

• 1 test per switch cases + 1 for default

• Default is always present, even if it is not written
28

Cannot cover
• Main

• Dates

• Randoms

• Network

• ...
29

–Robert C. Martin
“Every well designed system has at least one dirty
component, usually associated with main. Nothing
outside this component depends on anything inside
it. All dependencies point outward. This is where
you put switches, factories, and IOC.”
30
https://twitter.com/unclebobmartin/status/1122138039390806016

Quality
• 100% Code Coverage DO NOT ensure correctness

• With TDD Code Coverage should be 100%

• It is a hint

• it reveals what went wrong

• what we missed

• which cases we implemented but not planned
31

Summary


• AAA structure

• Code Coverage

• Test doubles
32

Serius Banking
test("deposit cash", () => {
const bank = new Bank()
bank.createAccount("John")
bank.deposit("John", 100)
expect(bank.get("John")).toBe(100)
})
class Bank {
deposit(name, amount) {
accounts.forEach(account => {
account.desposit += amount
})
}
}
33
🃏

Serius Banking
describe("regression tests", () => {
test("deposit cash into one single account", () => {
bank.createAccount("Maria")
expect(bank.get("Maria")).toBe(0)
})
})
34
🃏

Summary


• AAA structure

• Code Coverage


• Test doubles
35

Test Doubles
• Replaces data/object with one created by the test

• 5 types

• Dummy

• Stub

• Spy

• Mock

• Fake
36

Dummy
• Null, 0 or a plain value that can replace an argument
37
test("count created accounts", () => {
bank.createAccount("John", null)
expect(bank.count()).toBe(1)
})
class Bank {
createAccount(name, fiscalData) {
accounts.put(name, fiscalData)
}
}

Stub
• A value need for the test that the code uses
38
test("gives heads", () => {
const random = {
next() {
return 0
},
}
const result = flipCoin(random)
expect(result).toBe("head")
})
function flipCoin(random) {
if (random.next() < 0.5) return "head"
return "tails"
}

Spy
• Method that remembers its calls
39
test("hello world", () => {
const log = []
const outputSpy = message => {
log.push(message)
}
sayHello(outputSpy)
expect(log).toEqual(["hello world"])
})
function sayHello(output) {
output("hello world")
}

Mock
• A spy that validates correctness and knows the object
40
class DiskMock {
log = [];
move(cylinder) {
this.log.push('move', cylinder);
}
write(data) {
this.log.push('write', data)
}
isFormatted() {
return this.log.equals('move', 0, 'write', 0)
}
}
test('formats a disk', () => {
const disk = new DiskMock();
format(disk);
expect(disk.isFormatted()).toBeTrue();
})

Fake
• An functional object that replaces an original one
41
test("deposit cash", () => {
const db = new InMemoryDB()
const bank = new Bank(db)
})

Conﬁdence
• Test Doubles may Reduce Coverage

• Although, some cases are necessary

• Test Doubles Reduce Conﬁdence
42

Summary


• AAA structure

• Code Coverage


• Test doubles
43

Homework
• http://misko.hevery.com/code-reviewers-guide/
44

ES3-2020-07 Testing techniques

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