ESCAPE THE LEGACY CODE MATRIX

Vimercate 11/02/2017

mario.russo@lastminute.com

@rmarioo

and sleep at night

@rmarioo

QUIZ: Legacy code ?

A) Code difficult to change

B) Inherited code difficult to change

C) Valuable code we’re afraid to change

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LEGACY CODE

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• Is there a pragmatic approach ?

• Should I care about it ?

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Have you ever had these feelings ?

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• Fear / Under pressure

.. so I do changes inside the existing code

• Nervous ( i depend on… )

“engaged” with debugger , complex infrastructure

• Unsafe

Did i broke something ? Is this working ?

• Resigned

“Edit and pray”

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You are in the Matrix

…. and you are feeding the monster !!!

Diagnosis…

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Now take your choice..

@rmarioo 6

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The journey …of facing legacy code

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UNDERSTAND REFACTORCOVER

Each step has a different target.

Focus only on that target !

CHANGE

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• Use it

… before looking at the code!

• Find one thing you know

1. look for keywords

2. and trace the actions backward

Understand: How ?

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• Sketch refactoring

• Keep reading someone else code

Understand: How ?

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Cover: the main target

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• The 100% of test coverageCOVER

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Cover: where should i start ?

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if condition1

….

….

if condition2

…..

…..

if condition3

…..

…..

else

…..

…..

else

…..

…..

else

…..

…..

Start from shortest

to deepest branch

@rmarioo

Cover: test the unknown

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We assume to know what the code is supposed

to do

… but what if we don’t ?

• Test name ???

• Expected result ???

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Cover: Exploratory testing

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1. Write a test named “x”

2. Set any expected result

3. Run it and get a Failure

java.lang.AssertionError: expected:<null> but was:<plain text>

4. Copy the text and make it pass

5. Give a better name

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Shortcut: “Delimit your territory”

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Extract the code you want to change in a separate

section

- Smaller problem to solve

- Quicker way to the coverage

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Cover: Legacy code dilemma

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CHANGE

CODE

HAVE

TEST IN

PLACE

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… some special licences

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• Changes allowed only by IDE

refactoring

• Do not bother with code quality now

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Example : Subclass and override

1

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public class A {

public void do1(…) {

user = session.getAttribute(“user”);

...

}

public class ATest

{

@Test

public void do1WhenLogged() { }

private class TestableA extends A

{

@Override

protected boolean isLogged()

{

return true

}

}

} public void do1(…) {

...

logged = isLogged(“mario")

}

protected Boolean isLogged(..)

TEST CODE SOURCE CODE

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Modify phase: two targets

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REFACTOR CHANGE

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LET A TEST GUIDE US …

HARD TO CREATE

OR MAKE IT PASS ?

REFACTOR

APPLY THE

CHANGE

ADD A TEST

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Refactor: where to start ?

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if condition1

….

….

if condition2

…..

…..

if condition3

…..

…..

else

…..

…..

else

…..

…..

else

…..

…..

From deepest branch

@rmarioo

Yak shaving ..

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@rmarioo

Pair programming can help!

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• N: What are you doing?

• D: I am doing x and y and .. z

• N: Let’s choose one and complete it !

Write down x , y and z in the todo list

Single task editing allows to Getting things done

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Adding a new feature: a common mistake

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“Let’s put new feature inside this existing method

because it should happen at the same time”

Problem : … test old and new code together

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Ex. adding new feature: "Sprout class"

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1.

public void do1()

{

…

// new Feature(..).apply(…)

}

2. TDD

public class Feature

{

public void apply(…)

{

…

}

}3.

public void do1()

{

…

new Feature(..).apply(…)

}

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Pragmatic refactoring

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• Stop when the change is easy to apply

• Effort proportional to code “liveness”

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Don’t repeat yourself!

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• Split screen vertically TDD

• Continuous testing plugin

• Use shortcuts instead of repeating actions

• Small commits / steps

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Smells —> refactor —> steps & shortcuts

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Show me the code !

https://github.com/rmarioo/smells-to-refactoring

@rmarioo

References

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Books and publications

• Working Effectively with Legacy Code: Michael Feathers

• Refactoring: Improving the Design of Existing Code

• Sandro Mancuso – Testing and refactoring legacy code

• THE CODE WHISPERER - J. B. Rainsberger

Github projects

• Ugly trivia J. B. Rainsberger

• Videostore Robert Cecil Martin ( Uncle bob )

• Smells-to-refactoring Mario Russo

Thank you