What's new in Infection 0.9.0

Jul 1, 2018

Release: https://github.com/infection/infection/releases/tag/0.9.0

BC Breaks

Before upgrading, make sure you know about backward incompatible changes.

New features and enhancements


One of the most wanted feature! It allows you to configure what mutators to use or skip, by one or by “profiles”. This idea about Profiles is pretty much the same as in PHP-CS-Fixer (@PSR2, @symfony, etc.).

How does it work? The following configuration will use the @default profile, but turn off the @function_signature profile.
On top of that, it does not apply the TrueValue mutator on any classes that match the provided ignore patterns. In particular, TrueValue mutator does not mutate the code inside Full\NameSpaced\Class class and inside create() method of all SourceClass classes.

These ignores can also be added to profiles, to ensure infection is as flexible as you need it.

All profiles are prepended by an @ and in snake case, while all mutators are in PascalCase.

"mutators": {
"@default": true,
"@function_signature": false,
"TrueValue": {
"ignore": [

See how Mutators are grouped in Profiles

Prefixed PHAR

Starting from Infection 0.9.0, we will be shipping a prefixed PHAR by PHP-Scoper. What does it mean?

In a nutshell, PHP-Scoper adds a random prefix to each class’ namespace in the bundled code. It means that if you have PHP-Parser 3 in your project, but infection.phar has PHP-Parser 4 - there won’t be any conflicts anymore.

Now you can safely use PHAR distribution instead of requiring Infection by Composer.

Badge logger

Infection MSI

Thanks to our friends from Stryker - mutation testing framework for Javascript - Infection now has a Mutation Badge!

Add it to your project to show how awesome your are! Run mutation logger on CI (e.g. Travis) to update the badge automatically.

Per-Mutator logger

New perMutator logger can be configured in infection.json config. It shows a detailed report about Mutator effectiveness in a Markdown syntax.


Mutator Mutations Killed Escaped Errors MSI Covered MSI
ArrayItem 19 12 7 0 63 63
AssignmentEqual 4 3 1 0 75 75
TrueValue 51 29 15 0 57 66

Ignore MSI violations with zero mutations

If your project is quite big, mutation testing can take too much time to run it for each build on CI. In this case, it’s possible to run Infection just for the changed files.

Imagine, you want to have at least 80% MSI and you run Infection as

./infection.phar [...] --min-msi=80

When someone pushes the code that is not analyzed by Infection, e.g. new json file, Infection will create 0 Mutants and the MSI will be 0, so the build will fail.

To avoid this situations, there is a new option --ignore-msi-with-no-mutations just for that.

New Mutators


This mutator removes finally {} block from your try / catch / finally chain. Goal: to understand whether finally blocks are tested and bring any value.

By the way, did you know it is possible to not have any of the catch blocks in PHP? ;)

try {
} finally {

// string(3) "try"
// string(7) "finally"


This mutator replaces $a = preg_quote('text'); with $a = 'text';. Goal: to test whether preg_quote call is useful.

Set of Type Cast Mutators

These mutators remove type casting (e.g. $count = (int) $request->get(...) -> $count = $request->get(...)) in order to check whether this casting is useless or not.


This mutator does the following:

- [$a->foo => $b->bar]
+ [$a->foo > $b->bar]

It applies only for keys and values that have side effects (read explicit or implicit function calls).

Firstly, this mutation changes the keys of the array, which is a good thing to check your tests. Secondly, it changes values, but without removing function/method calls. So if you are just asserting on method calls of your Mock objects and do not test keys/values - mutation won’t be killed!


- yield $a => $b;
+ yield $a > $b;

The goal is clear again - the key and the value of the returned value are changed, it must be caught by your test.


It replaces all variants of +=, *=, .=, etc. with just =.

- $dql .= 'GROUP BY status';
+ $dql = 'GROUP BY status';


This mutator do the following:

- for ($i = 0; $i < 10; $i++) {...}
+ for ($i = 0; false; $i++) {...}

Improvements for mutators

We have improved our Mutators and added \ReflectionClass() information to them. It means they are smarter now, and we can avoid many useless mutations we had previously. For example, for this code:

interface Doable
public function do(): void;

class Foo implements Doable
public function do(): void {}

the following mutation is incorrect:

class Foo implements Doable
- public function do(): void {}
+ protected function do(): void {}

and leads to Fatal error: Access level to Foo::do() must be public (as in class Doable)....


We have also replaced our custom logic of disabling Xdebug with the new composer tool: composer/xdebug-handler. Check out this great library!

It can automatically restart any process with disabled Xdebug in order to achieve the best performance.

If you use and/or like Infection, please make sure to give us a star:

Also, you can follow us on Twitter: https://twitter.com/infection_php

Thank you @infection/core and all contributors for 0.9.0 release. This is a great day for Mutation Testing in PHP.