diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 06739d4..85ef7d9 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,13 +8,13 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macOS-latest]
-        php-version: ['7.4']
-    name: 'PHPUnit - PHP/${{ matrix.php-version }} - OS/${{ matrix.os }}'
+        php-version: ['7.4', '8.0']
+    name: 'PHPUnit'
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
       - name: Setup PHP
-        uses: shivammathur/setup-php@v1
+        uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php-version }}
           extensions: mbstring, intl
@@ -23,7 +23,7 @@ jobs:
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"
       - name: Cache dependencies
-        uses: actions/cache@v1
+        uses: actions/cache@v2
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
@@ -39,13 +39,13 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        php-version: ['7.4']
-    name: 'Psalm - PHP/${{ matrix.php-version }}'
+        php-version: ['7.4', '8.0']
+    name: 'Psalm'
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        uses: actions/checkout@v2
       - name: Setup PHP
-        uses: shivammathur/setup-php@v1
+        uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php-version }}
           extensions: mbstring, intl
@@ -53,7 +53,7 @@ jobs:
         id: composer-cache
         run: echo "::set-output name=dir::$(composer config cache-files-dir)"
       - name: Cache dependencies
-        uses: actions/cache@v1
+        uses: actions/cache@v2
         with:
           path: ${{ steps.composer-cache.outputs.dir }}
           key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
@@ -61,4 +61,31 @@ jobs:
       - name: Install Dependencies
         run: composer install
       - name: Psalm
-        run: vendor/bin/psalm
+        run: vendor/bin/psalm --shepherd
+  cs:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php-version: ['7.4']
+    name: 'CS'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          extensions: mbstring, intl
+      - name: Get Composer Cache Directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-${{ matrix.php-version }}-composer-${{ hashFiles('**/composer.json') }}
+          restore-keys: ${{ runner.os }}-${{ matrix.php-version }}-composer-
+      - name: Install Dependencies
+        run: composer install --no-progress
+      - name: CS
+        run: vendor/bin/php-cs-fixer fix --diff --dry-run --diff-format udiff
diff --git a/.php_cs.dist b/.php_cs.dist
new file mode 100644
index 0000000..1431d66
--- /dev/null
+++ b/.php_cs.dist
@@ -0,0 +1,6 @@
+<?php
+
+return Innmind\CodingStandard\CodingStandard::config([
+    'tests',
+    'src',
+]);
diff --git a/README.md b/README.md
index 9abd081..bf10adc 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,8 @@
 # UrlTemplate
 
-| `develop` |
-|-----------|
-| [![codecov](https://codecov.io/gh/Innmind/UrlTemplate/branch/develop/graph/badge.svg)](https://codecov.io/gh/Innmind/UrlTemplate) |
-| [![Build Status](https://github.com/Innmind/UrlTemplate/workflows/CI/badge.svg)](https://github.com/Innmind/UrlTemplate/actions?query=workflow%3ACI) |
+[![Build Status](https://github.com/innmind/urltemplate/workflows/CI/badge.svg?branch=master)](https://github.com/innmind/urltemplate/actions?query=workflow%3ACI)
+[![codecov](https://codecov.io/gh/innmind/urltemplate/branch/develop/graph/badge.svg)](https://codecov.io/gh/innmind/urltemplate)
+[![Type Coverage](https://shepherd.dev/github/innmind/urltemplate/coverage.svg)](https://shepherd.dev/github/innmind/urltemplate)
 
 [RFC6570](https://tools.ietf.org/html/rfc6570) implementation.
 
diff --git a/composer.json b/composer.json
index 67b8389..31208c5 100644
--- a/composer.json
+++ b/composer.json
@@ -15,7 +15,7 @@
         "issues": "http://github.com/Innmind/UrlTemplate/issues"
     },
     "require": {
-        "php": "~7.4",
+        "php": "~7.4|~8.0",
         "innmind/url": "~3.0",
         "innmind/immutable": "~3.1"
     },
@@ -30,8 +30,9 @@
         }
     },
     "require-dev": {
-        "phpunit/phpunit": "~8.0",
-        "giorgiosironi/eris": "^0.11.0",
-        "vimeo/psalm": "~3.7.0"
+        "phpunit/phpunit": "~9.0",
+        "vimeo/psalm": "~4.4",
+        "innmind/black-box": "^4.16",
+        "innmind/coding-standard": "^1.1"
     }
 }
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 148afda..51d31c5 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,19 +1,17 @@
 <?xml version="1.0" encoding="UTF-8"?>
-
-<phpunit colors="true" bootstrap="vendor/autoload.php">
-    <testsuites>
-        <testsuite name="Test suite">
-            <directory>./tests</directory>
-        </testsuite>
-    </testsuites>
-
-    <filter>
-        <whitelist>
-            <directory>.</directory>
-            <exclude>
-                <directory>./tests</directory>
-                <directory>./vendor</directory>
-            </exclude>
-        </whitelist>
-    </filter>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" colors="true" bootstrap="vendor/autoload.php" printerClass="Innmind\BlackBox\PHPUnit\ResultPrinterV9" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+  <coverage>
+    <include>
+      <directory>.</directory>
+    </include>
+    <exclude>
+      <directory>./tests</directory>
+      <directory>./vendor</directory>
+    </exclude>
+  </coverage>
+  <testsuites>
+    <testsuite name="Test suite">
+      <directory>./tests</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>
diff --git a/psalm.xml b/psalm.xml
index 408036f..3240886 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <psalm
-    totallyTyped="true"
+    errorLevel="1"
     resolveFromConfigFile="true"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
@@ -12,8 +12,4 @@
             <directory name="vendor" />
         </ignoreFiles>
     </projectFiles>
-
-    <issueHandlers>
-        <LessSpecificReturnType errorLevel="info" />
-    </issueHandlers>
 </psalm>
diff --git a/src/Expression/Level1.php b/src/Expression/Level1.php
index 61b4974..ca483b5 100644
--- a/src/Expression/Level1.php
+++ b/src/Expression/Level1.php
@@ -27,9 +27,6 @@ public function __construct(Name $name)
         $this->encode = new UrlEncode;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{[a-zA-Z0-9_]+\}$~')) {
@@ -39,9 +36,6 @@ public static function of(Str $string): Expression
         return new self(new Name($string->trim('{}')->toString()));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         if (!$variables->contains($this->name->toString())) {
diff --git a/src/Expression/Level2/Fragment.php b/src/Expression/Level2/Fragment.php
index 7af8230..61f6b28 100644
--- a/src/Expression/Level2/Fragment.php
+++ b/src/Expression/Level2/Fragment.php
@@ -28,9 +28,6 @@ public function __construct(Name $name)
         $this->encode = UrlEncode::allowReservedCharacters();
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{#[a-zA-Z0-9_]+\}$~')) {
@@ -40,9 +37,6 @@ public static function of(Str $string): Expression
         return new self(new Name($string->trim('{#}')->toString()));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         if (!$variables->contains($this->name->toString())) {
diff --git a/src/Expression/Level2/Reserved.php b/src/Expression/Level2/Reserved.php
index 226a5ea..63e1a0a 100644
--- a/src/Expression/Level2/Reserved.php
+++ b/src/Expression/Level2/Reserved.php
@@ -28,9 +28,6 @@ public function __construct(Name $name)
         $this->encode = UrlEncode::allowReservedCharacters();
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{\+[a-zA-Z0-9_]+\}$~')) {
@@ -40,9 +37,6 @@ public static function of(Str $string): Expression
         return new self(new Name($string->trim('{+}')->toString()));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         if (!$variables->contains($this->name->toString())) {
diff --git a/src/Expression/Level3.php b/src/Expression/Level3.php
index 1725231..d370778 100644
--- a/src/Expression/Level3.php
+++ b/src/Expression/Level3.php
@@ -37,9 +37,6 @@ public function __construct(Name ...$names)
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -58,9 +55,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         $expanded = $this->expressions->mapTo(
@@ -73,6 +67,7 @@ public function expand(Map $variables): string
 
     public function regex(): string
     {
+        /** @psalm-suppress InvalidArgument */
         return $this->regex ?? $this->regex = join(
             ',',
             $this->names->mapTo(
diff --git a/src/Expression/Level3/Fragment.php b/src/Expression/Level3/Fragment.php
index 1e678b2..bb52f24 100644
--- a/src/Expression/Level3/Fragment.php
+++ b/src/Expression/Level3/Fragment.php
@@ -39,9 +39,6 @@ public function __construct(Name ...$names)
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{#[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -60,9 +57,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         $expanded = $this->expressions->mapTo(
diff --git a/src/Expression/Level3/Label.php b/src/Expression/Level3/Label.php
index c9fa0eb..73d89a6 100644
--- a/src/Expression/Level3/Label.php
+++ b/src/Expression/Level3/Label.php
@@ -39,9 +39,6 @@ public function __construct(Name ...$names)
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{\.[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -60,9 +57,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         $expanded = $this->expressions->mapTo(
diff --git a/src/Expression/Level3/NamedValues.php b/src/Expression/Level3/NamedValues.php
index cb95f0f..530bd37 100644
--- a/src/Expression/Level3/NamedValues.php
+++ b/src/Expression/Level3/NamedValues.php
@@ -41,9 +41,6 @@ public function __construct(string $lead, string $separator, Name ...$names)
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         throw new \LogicException('should not be used directly');
@@ -57,9 +54,6 @@ public static function keyOnlyWhenEmpty(string $lead, string $separator, Name ..
         return $self;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         /** @var Sequence<string> */
diff --git a/src/Expression/Level3/Parameters.php b/src/Expression/Level3/Parameters.php
index 40baf30..247915d 100644
--- a/src/Expression/Level3/Parameters.php
+++ b/src/Expression/Level3/Parameters.php
@@ -24,9 +24,6 @@ public function __construct(Name ...$names)
         $this->expression = NamedValues::keyOnlyWhenEmpty(';', ';', ...$names);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{;[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -45,9 +42,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return $this->expression->expand($variables);
diff --git a/src/Expression/Level3/Path.php b/src/Expression/Level3/Path.php
index 34a1a41..0e97a90 100644
--- a/src/Expression/Level3/Path.php
+++ b/src/Expression/Level3/Path.php
@@ -39,9 +39,6 @@ public function __construct(Name ...$names)
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{/[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -60,9 +57,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return join(
diff --git a/src/Expression/Level3/Query.php b/src/Expression/Level3/Query.php
index e45d4ac..a442c23 100644
--- a/src/Expression/Level3/Query.php
+++ b/src/Expression/Level3/Query.php
@@ -24,9 +24,6 @@ public function __construct(Name ...$names)
         $this->expression = new NamedValues('?', '&', ...$names);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{\?[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -45,9 +42,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return $this->expression->expand($variables);
diff --git a/src/Expression/Level3/QueryContinuation.php b/src/Expression/Level3/QueryContinuation.php
index 0b7bb89..fdb5ee6 100644
--- a/src/Expression/Level3/QueryContinuation.php
+++ b/src/Expression/Level3/QueryContinuation.php
@@ -24,9 +24,6 @@ public function __construct(Name ...$names)
         $this->expression = new NamedValues('&', '&', ...$names);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{\&[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -45,9 +42,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return $this->expression->expand($variables);
diff --git a/src/Expression/Level3/Reserved.php b/src/Expression/Level3/Reserved.php
index b697818..3412069 100644
--- a/src/Expression/Level3/Reserved.php
+++ b/src/Expression/Level3/Reserved.php
@@ -39,9 +39,6 @@ public function __construct(Name ...$names)
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if (!$string->matches('~^\{\+[a-zA-Z0-9_]+(,[a-zA-Z0-9_]+)+\}$~')) {
@@ -60,9 +57,6 @@ public static function of(Str $string): Expression
         return new self(...unwrap($names));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         $expanded = $this->expressions->mapTo(
diff --git a/src/Expression/Level4.php b/src/Expression/Level4.php
index 33399b8..4a511f1 100644
--- a/src/Expression/Level4.php
+++ b/src/Expression/Level4.php
@@ -37,9 +37,6 @@ public function __construct(Name $name)
         $this->expression = new Level1($name);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{[a-zA-Z0-9_]+\}$~')) {
@@ -116,7 +113,7 @@ public function withSeparator(string $separator): self
      */
     public function withExpression(string $expression): self
     {
-        if (!is_a($expression, Expression::class, true)) {
+        if (!\is_a($expression, Expression::class, true)) {
             throw new DomainException($expression);
         }
 
@@ -126,9 +123,6 @@ public function withExpression(string $expression): self
         return $self;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         if (!$variables->contains($this->name->toString())) {
@@ -217,6 +211,7 @@ private function expandList(Map $variables, ...$variablesToExpand): string
             return $this->explodeList($variables, $variablesToExpand);
         }
 
+        /** @var Sequence<scalar> */
         $flattenedVariables = Sequence::of('scalar|array', ...$variablesToExpand)->reduce(
             Sequence::of('scalar'),
             static function(Sequence $values, $variableToExpand): Sequence {
@@ -229,8 +224,9 @@ static function(Sequence $values, $variableToExpand): Sequence {
                 return ($values)($variableToExpand);
             },
         );
+
         $expanded = $flattenedVariables
-            ->map(function(string $variableToExpand) use ($variables): string {
+            ->map(function($variableToExpand) use ($variables): string {
                 // here we use the level1 expression to transform the variable to
                 // be expanded to its string representation
                 return $this->expression->expand(
diff --git a/src/Expression/Level4/Composite.php b/src/Expression/Level4/Composite.php
index 3357a68..9e7a277 100644
--- a/src/Expression/Level4/Composite.php
+++ b/src/Expression/Level4/Composite.php
@@ -73,9 +73,6 @@ static function(Expression $level4, Str $expression): Expression {
             );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         $expanded = $this->expressions->mapTo(
diff --git a/src/Expression/Level4/Fragment.php b/src/Expression/Level4/Fragment.php
index 12f9dc3..42fa2a9 100644
--- a/src/Expression/Level4/Fragment.php
+++ b/src/Expression/Level4/Fragment.php
@@ -29,9 +29,6 @@ public function __construct(Name $name)
             ->withExpression(Level2\Reserved::class);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{#[a-zA-Z0-9_]+\}$~')) {
@@ -93,9 +90,6 @@ public function regex(): string
         return $this->expression->regex();
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return $this->expression->expand($variables);
diff --git a/src/Expression/Level4/Label.php b/src/Expression/Level4/Label.php
index 7fbca13..84721c9 100644
--- a/src/Expression/Level4/Label.php
+++ b/src/Expression/Level4/Label.php
@@ -26,9 +26,6 @@ public function __construct(Name $name)
         $this->expression = (new Level4($name))->withLead('.');
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{\.[a-zA-Z0-9_]+\}$~')) {
@@ -83,9 +80,6 @@ public function add(Str $pattern): Composite
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return $this->expression->expand($variables);
diff --git a/src/Expression/Level4/Parameters.php b/src/Expression/Level4/Parameters.php
index 2fe71a4..45cab79 100644
--- a/src/Expression/Level4/Parameters.php
+++ b/src/Expression/Level4/Parameters.php
@@ -38,9 +38,6 @@ public function __construct(Name $name)
         $this->expression = new Level1($name);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{;[a-zA-Z0-9_]+\}$~')) {
@@ -181,6 +178,7 @@ private function expandList(Map $variables, ...$variablesToExpand): string
             return $this->explodeList($variables, $variablesToExpand);
         }
 
+        /** @var Sequence<scalar> */
         $flattenedVariables = Sequence::of('scalar|array', ...$variablesToExpand)->reduce(
             Sequence::of('scalar'),
             static function(Sequence $values, $variableToExpand): Sequence {
diff --git a/src/Expression/Level4/Path.php b/src/Expression/Level4/Path.php
index 6b2f106..eb40380 100644
--- a/src/Expression/Level4/Path.php
+++ b/src/Expression/Level4/Path.php
@@ -26,9 +26,6 @@ public function __construct(Name $name)
         $this->expression = (new Level4($name))->withLead('/');
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{/[a-zA-Z0-9_]+\}$~')) {
@@ -83,9 +80,6 @@ public function add(Str $pattern): Composite
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return $this->expression->expand($variables);
diff --git a/src/Expression/Level4/Query.php b/src/Expression/Level4/Query.php
index 66242c1..dfd61cd 100644
--- a/src/Expression/Level4/Query.php
+++ b/src/Expression/Level4/Query.php
@@ -38,9 +38,6 @@ public function __construct(Name $name)
         $this->expression = new Level1($name);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{\?[a-zA-Z0-9_]+\}$~')) {
@@ -142,7 +139,7 @@ public function regex(): string
             $regex = $this->expression->regex();
         }
 
-        return $this->regex = sprintf(
+        return $this->regex = \sprintf(
             '\?%s=%s',
             $this->name->toString(),
             $regex,
@@ -181,6 +178,7 @@ private function expandList(Map $variables, ...$variablesToExpand): string
             return $this->explodeList($variables, $variablesToExpand);
         }
 
+        /** @var Sequence<scalar> */
         $flattenedVariables = Sequence::of('scalar|array', ...$variablesToExpand)->reduce(
             Sequence::of('scalar'),
             static function(Sequence $values, $variableToExpand): Sequence {
diff --git a/src/Expression/Level4/QueryContinuation.php b/src/Expression/Level4/QueryContinuation.php
index 216023d..a2b05bb 100644
--- a/src/Expression/Level4/QueryContinuation.php
+++ b/src/Expression/Level4/QueryContinuation.php
@@ -38,9 +38,6 @@ public function __construct(Name $name)
         $this->expression = new Level1($name);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{\&[a-zA-Z0-9_]+\}$~')) {
@@ -181,6 +178,7 @@ private function expandList(Map $variables, ...$variablesToExpand): string
             return $this->explodeList($variables, $variablesToExpand);
         }
 
+        /** @var Sequence<scalar> */
         $flattenedVariables = Sequence::of('scalar|array', ...$variablesToExpand)->reduce(
             Sequence::of('scalar'),
             static function(Sequence $values, $variableToExpand): Sequence {
diff --git a/src/Expression/Level4/Reserved.php b/src/Expression/Level4/Reserved.php
index 1db65bf..b74d033 100644
--- a/src/Expression/Level4/Reserved.php
+++ b/src/Expression/Level4/Reserved.php
@@ -35,9 +35,6 @@ public function __construct(Name $name)
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public static function of(Str $string): Expression
     {
         if ($string->matches('~^\{\+[a-zA-Z0-9_]+\}$~')) {
@@ -96,9 +93,6 @@ public function add(Str $pattern): Composite
         );
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function expand(Map $variables): string
     {
         return $this->expression->expand($variables);
diff --git a/src/Template.php b/src/Template.php
index 3168c9f..7e41fd0 100644
--- a/src/Template.php
+++ b/src/Template.php
@@ -50,7 +50,7 @@ public function expand(Map $variables): Url
 
         $url = $this->expressions->reduce(
             $this->template,
-            function(Str $template, Expression $expression) use ($variables): Str {
+            static function(Str $template, Expression $expression) use ($variables): Str {
                 return $template->replace(
                     $expression->toString(),
                     $expression->expand($variables),
@@ -106,6 +106,9 @@ public function toString(): string
     /**
      * Recursively find the expressions as Str::capture doesnt capture all of
      * them at the same time
+     * @param Sequence<string> $expressions
+     *
+     * @return Sequence<string>
      */
     private function extractExpressions(
         Sequence $expressions,
@@ -133,7 +136,10 @@ private function regex(): string
                 ->reduce(
                     $this->template->replace('~', '\~'),
                     static function(Str $template, Expression $expression) use (&$i): Str {
-                        /** @psalm-suppress MixedOperand */
+                        /**
+                         * @psalm-suppress MixedOperand
+                         * @psalm-suppress MixedAssignment
+                         */
                         ++$i;
 
                         return $template->replace(
@@ -146,7 +152,10 @@ static function(Str $template, Expression $expression) use (&$i): Str {
             $template = $this->expressions->reduce(
                 $template,
                 static function(Str $template, Expression $expression) use (&$j): Str {
-                    /** @psalm-suppress MixedOperand */
+                    /**
+                     * @psalm-suppress MixedOperand
+                     * @psalm-suppress MixedAssignment
+                     */
                     ++$j;
 
                     return $template->replace(
diff --git a/src/UrlEncode.php b/src/UrlEncode.php
index 91d4ab3..b75df39 100644
--- a/src/UrlEncode.php
+++ b/src/UrlEncode.php
@@ -15,14 +15,6 @@ public function __construct()
         $this->safeCharacters = Str::of('');
     }
 
-    public static function allowReservedCharacters(): self
-    {
-        $self = new self;
-        $self->safeCharacters = Str::of(':/?#[]@!$&\'()*+,;=');
-
-        return $self;
-    }
-
     public function __invoke(string $string): string
     {
         if ($this->safeCharacters->empty()) {
@@ -55,4 +47,12 @@ public function __invoke(string $string): string
 
         return \rawurlencode($string->toString());
     }
+
+    public static function allowReservedCharacters(): self
+    {
+        $self = new self;
+        $self->safeCharacters = Str::of(':/?#[]@!$&\'()*+,;=');
+
+        return $self;
+    }
 }
diff --git a/tests/Expression/Level4/FragmentTest.php b/tests/Expression/Level4/FragmentTest.php
index 65fdf72..a475f52 100644
--- a/tests/Expression/Level4/FragmentTest.php
+++ b/tests/Expression/Level4/FragmentTest.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class FragmentTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/Level4/LabelTest.php b/tests/Expression/Level4/LabelTest.php
index 444de53..2775ecb 100644
--- a/tests/Expression/Level4/LabelTest.php
+++ b/tests/Expression/Level4/LabelTest.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class LabelTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/Level4/ParametersTest.php b/tests/Expression/Level4/ParametersTest.php
index 27e7ad4..ae6d2a4 100644
--- a/tests/Expression/Level4/ParametersTest.php
+++ b/tests/Expression/Level4/ParametersTest.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class ParametersTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/Level4/PathTest.php b/tests/Expression/Level4/PathTest.php
index 3b942fe..b0e7bf3 100644
--- a/tests/Expression/Level4/PathTest.php
+++ b/tests/Expression/Level4/PathTest.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class PathTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/Level4/QueryContinuationTest.php b/tests/Expression/Level4/QueryContinuationTest.php
index 7aac88a..4755e51 100644
--- a/tests/Expression/Level4/QueryContinuationTest.php
+++ b/tests/Expression/Level4/QueryContinuationTest.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class QueryContinuationTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/Level4/QueryTest.php b/tests/Expression/Level4/QueryTest.php
index 246d59c..b7471e2 100644
--- a/tests/Expression/Level4/QueryTest.php
+++ b/tests/Expression/Level4/QueryTest.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class QueryTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/Level4/ReservedTest.php b/tests/Expression/Level4/ReservedTest.php
index a0c9d5f..57f8dee 100644
--- a/tests/Expression/Level4/ReservedTest.php
+++ b/tests/Expression/Level4/ReservedTest.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class ReservedTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/Level4Test.php b/tests/Expression/Level4Test.php
index 0a8799c..19f4e61 100644
--- a/tests/Expression/Level4Test.php
+++ b/tests/Expression/Level4Test.php
@@ -15,14 +15,14 @@
     Str,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class Level4Test extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
@@ -50,7 +50,7 @@ public function testStringCast()
     public function testThrowWhenNegativeLimit()
     {
         $this
-            ->forAll(Generator\neg())
+            ->forAll(Set\Integers::below(1))
             ->then(function(int $int): void {
                 $this->expectException(DomainException::class);
 
diff --git a/tests/Expression/NameTest.php b/tests/Expression/NameTest.php
index 6fcbeea..5e6c3c2 100644
--- a/tests/Expression/NameTest.php
+++ b/tests/Expression/NameTest.php
@@ -8,22 +8,23 @@
     Exception\DomainException,
 };
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class NameTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testInterface()
     {
         $this
-            ->forAll(Generator\string())
-            ->when(static function(string $string): bool {
-                return (bool) preg_match('~[a-zA-Z0-9_]+~', $string);
-            })
+            ->forAll(
+                Set\Strings::atLeast(1)->filter(static function(string $string): bool {
+                    return (bool) \preg_match('~[a-zA-Z0-9_]+~', $string);
+                }),
+            )
             ->then(function(string $string): void {
                 $this->assertSame($string, (new Name($string))->toString());
             });
@@ -32,10 +33,11 @@ public function testInterface()
     public function testThrowWhenInvalidName()
     {
         $this
-            ->forAll(Generator\string())
-            ->when(static function(string $string): bool {
-                return !preg_match('~[a-zA-Z0-9_]+~', $string);
-            })
+            ->forAll(
+                Set\Strings::any()->filter(static function(string $string): bool {
+                    return (bool) !\preg_match('~[a-zA-Z0-9_]+~', $string);
+                }),
+            )
             ->then(function(string $string): void {
                 $this->expectException(DomainException::class);
                 $this->expectExceptionMessage($string);
diff --git a/tests/TemplateTest.php b/tests/TemplateTest.php
index 75d1824..0927047 100644
--- a/tests/TemplateTest.php
+++ b/tests/TemplateTest.php
@@ -13,7 +13,6 @@
     Map,
     Sequence,
 };
-use function Innmind\Immutable\first;
 use PHPUnit\Framework\TestCase;
 
 class TemplateTest extends TestCase
diff --git a/tests/UrlEncodeTest.php b/tests/UrlEncodeTest.php
index bc29c86..975dd73 100644
--- a/tests/UrlEncodeTest.php
+++ b/tests/UrlEncodeTest.php
@@ -5,30 +5,30 @@
 
 use Innmind\UrlTemplate\UrlEncode;
 use PHPUnit\Framework\TestCase;
-use Eris\{
-    Generator,
-    TestTrait,
+use Innmind\BlackBox\{
+    PHPUnit\BlackBox,
+    Set,
 };
 
 class UrlEncodeTest extends TestCase
 {
-    use TestTrait;
+    use BlackBox;
 
     public function testStandardEncode()
     {
         $this
-            ->forAll(Generator\string())
+            ->forAll(Set\Strings::any())
             ->then(function(string $string): void {
                 $encode = new UrlEncode;
 
-                $this->assertSame(rawurlencode($string), $encode($string));
+                $this->assertSame(\rawurlencode($string), $encode($string));
             });
     }
 
     public function testSafeCharactersAreNotEncoded()
     {
         $this
-            ->forAll(Generator\elements(
+            ->forAll(Set\Elements::of(
                 ':',
                 '/',
                 '?',