diff --git a/.gitignore b/.gitignore
index cdd7d7b..a45c104 100644
--- a/.gitignore
+++ b/.gitignore
@@ -30,6 +30,12 @@
 /.phpunit.result.cache
 
 
+# ------------------------------------------------------------------------------
+### Infection
+# ------------------------------------------------------------------------------
+/infection.json
+
+
 # ------------------------------------------------------------------------------
 ### PHP Coding Standards Fixer
 # ------------------------------------------------------------------------------
diff --git a/CHANGELOG.md b/CHANGELOG.md
index c32cb66..78ad0c2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ Common and useful classes, methods, exceptions etc.
 
 1. Phing > remove old and unused tools
 2. Phing > configuration > minor updates
+3. Implement Mutation Testing Framework (infection/infection package)
 
 # 1.0.1
 
diff --git a/composer.json b/composer.json
index c19df0f..f39c07b 100644
--- a/composer.json
+++ b/composer.json
@@ -22,6 +22,7 @@
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.14",
+        "infection/infection": "^0.11.4",
         "phpunit/phpunit": "^8.0",
         "sebastian/phpcpd": "^4.1",
         "squizlabs/php_codesniffer": " ^2.9"
diff --git a/docs/Development.md b/docs/Development.md
index 7f60fb0..211e9f4 100644
--- a/docs/Development.md
+++ b/docs/Development.md
@@ -112,6 +112,46 @@ docker-compose run --rm phpunit --verbose --no-coverage
 I have to use [squizlabs/php_codesniffer](https://packagist.org/packages/squizlabs/php_codesniffer) `^2.9` instead of
 `^3.3`, because [Phing doesn't support 3.x PHP_CodeSniffer](https://github.com/phingofficial/phing/issues/716).
 
+# Mutation Tests
+
+Served by [Infection — Mutation Testing Framework](https://infection.github.io).
+
+### Running tests
+
+```bash
+docker-compose exec php vendor/bin/infection --threads=5
+```
+
+or
+
+```bash
+docker-compose exec php phing -f phing/tests.xml test:infection
+```
+
+### Result of testing
+
+##### Terminal
+
+Example of output:
+```bash
+125 mutations were generated:
+     105 mutants were killed
+       3 mutants were not covered by tests
+       5 covered mutants were not detected
+       0 errors were encountered
+      12 time outs were encountered
+
+Metrics:
+         Mutation Score Indicator (MSI): 93%
+         Mutation Code Coverage: 97%
+         Covered Code MSI: 95%
+```
+
+##### Stored in `build/reports/infection` directory
+
+* `build/reports/infection/infection-log.txt`
+* `build/reports/infection/summary-log.txt`
+
 # Other
 
 Rebuild project and run tests by running command:
diff --git a/infection.json.dist b/infection.json.dist
new file mode 100644
index 0000000..06b8a4c
--- /dev/null
+++ b/infection.json.dist
@@ -0,0 +1,13 @@
+{
+    "timeout": 10,
+    "source": {
+        "directories": [
+            "src"
+        ]
+    },
+    "logs": {
+        "text": "build/reports/infection/infection-log.txt",
+        "summary": "build/reports/infection/summary-log.txt",
+        "debug": "build/reports/infection/debug-log.txt"
+    }
+}
diff --git a/phing/properties.dist b/phing/properties.dist
index d1aa6d2..3a49281 100644
--- a/phing/properties.dist
+++ b/phing/properties.dist
@@ -77,5 +77,7 @@ tests.database = ${dir.data.temporary}/database.sqlite
 
 # Paths of frameworks used to run tests:
 # - PHPUnit (unit tests)
+# - Infection (mutation tests)
 #
-tests.phpunit.command = ./vendor/bin/phpunit --verbose
+tests.phpunit.command = ./vendor/bin/phpunit --verbose --no-coverage
+tests.mutation.command = ./vendor/bin/infection --threads=5
diff --git a/phing/tests.xml b/phing/tests.xml
index a03b709..3f97f01 100644
--- a/phing/tests.xml
+++ b/phing/tests.xml
@@ -48,7 +48,7 @@
 
     <!-- Test target -->
     <target name="build:test"
-            depends="test:phpunit"
+            depends="test:phpunit, test:infection"
     />
 
     <!-- Symfony2 code sniffer -->
@@ -74,6 +74,11 @@
         <exec command="${tests.phpunit.command}" passthru="true"/>
     </target>
 
+    <!-- Run mutation testing -->
+    <target name="test:infection" depends="build:prepare">
+        <exec command="${tests.mutation.command}" passthru="true"/>
+    </target>
+
     <!-- Project build clean -->
     <target name="build:clean">
         <if>