diff --git a/CHANGELOG.md b/CHANGELOG.md
index a7308ec..66315e3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## [Unreleased]
+
+### Added
+
+- `Innmind\Server\Control\Server\Process\Builder`, internal tool to mock processes
+
 ## 7.0.0 - 2026-01-31
 
 ### Changed
diff --git a/src/Server/Process/Builder.php b/src/Server/Process/Builder.php
new file mode 100644
index 0000000..9f398b5
--- /dev/null
+++ b/src/Server/Process/Builder.php
@@ -0,0 +1,162 @@
+<?php
+declare(strict_types = 1);
+
+namespace Innmind\Server\Control\Server\Process;
+
+use Innmind\Server\Control\Server\{
+    Process,
+    Process\Output\Chunk,
+    Process\Output\Type,
+};
+use Innmind\Immutable\{
+    Sequence,
+    Str,
+};
+
+/**
+ * @internal
+ */
+final class Builder
+{
+    /**
+     * @psalm-mutation-free
+     *
+     * @param ?int<2, max> $pid
+     */
+    private function __construct(
+        private ?int $pid,
+        private Success|Signaled|TimedOut|Failed $result,
+    ) {
+    }
+
+    /**
+     * @internal
+     * @psalm-pure
+     *
+     * @param int<2, max> $pid
+     */
+    #[\NoDiscard]
+    public static function foreground(int $pid): self
+    {
+        return new self($pid, new Success(Sequence::of()));
+    }
+
+    /**
+     * @internal
+     * @psalm-pure
+     */
+    #[\NoDiscard]
+    public static function background(): self
+    {
+        return new self(null, new Success(Sequence::of()));
+    }
+
+    /**
+     * @psalm-mutation-free
+     *
+     * @param Sequence<Chunk>|list<array{string, 'output'|'error'}> $output
+     */
+    #[\NoDiscard]
+    public function success(Sequence|array|null $output = null): self
+    {
+        return new self(
+            $this->pid,
+            new Success(self::output($output)),
+        );
+    }
+
+    /**
+     * @psalm-mutation-free
+     *
+     * @param Sequence<Chunk>|list<array{string, 'output'|'error'}> $output
+     */
+    #[\NoDiscard]
+    public function signaled(Sequence|array|null $output = null): self
+    {
+        return new self(
+            $this->pid,
+            new Signaled(self::output($output)),
+        );
+    }
+
+    /**
+     * @psalm-mutation-free
+     *
+     * @param Sequence<Chunk>|list<array{string, 'output'|'error'}> $output
+     */
+    #[\NoDiscard]
+    public function timedOut(Sequence|array|null $output = null): self
+    {
+        return new self(
+            $this->pid,
+            new TimedOut(self::output($output)),
+        );
+    }
+
+    /**
+     * @psalm-mutation-free
+     *
+     * @param int<1, 255> $exitCode
+     * @param Sequence<Chunk>|list<array{string, 'output'|'error'}> $output
+     */
+    #[\NoDiscard]
+    public function failed(int $exitCode = 1, Sequence|array|null $output = null): self
+    {
+        return new self(
+            $this->pid,
+            new Failed(
+                new ExitCode($exitCode),
+                self::output($output),
+            ),
+        );
+    }
+
+    /**
+     * @internal
+     */
+    #[\NoDiscard]
+    public function build(): Process
+    {
+        $pid = $this->pid;
+        $result = $this->result;
+
+        /**
+         * This a trick to not expose any mock contructor on the Process class.
+         *
+         * @psalm-suppress PossiblyNullFunctionCall
+         * @psalm-suppress MixedReturnStatement
+         * @psalm-suppress InaccessibleMethod
+         */
+        return (\Closure::bind(
+            static fn() => new Process(new Mock($pid, $result)),
+            null,
+            Process::class,
+        ))();
+    }
+
+    /**
+     * @psalm-pure
+     *
+     * @param Sequence<Chunk>|list<array{string, 'output'|'error'}> $output
+     *
+     * @return Sequence<Chunk>
+     */
+    private static function output(Sequence|array|null $output = null): Sequence
+    {
+        if (\is_null($output)) {
+            return Sequence::of();
+        }
+
+        if (\is_array($output)) {
+            return Sequence::of(...$output)->map(static fn($pair) => Chunk::of(
+                Str::of($pair[0]),
+                match ($pair[1]) {
+                    'output' => Type::output,
+                    'error' => Type::error,
+                },
+            ));
+        }
+
+        return $output;
+    }
+}
diff --git a/src/Server/Process/Failed.php b/src/Server/Process/Failed.php
index cc36c09..82e47e6 100644
--- a/src/Server/Process/Failed.php
+++ b/src/Server/Process/Failed.php
@@ -5,6 +5,9 @@
 
 use Innmind\Immutable\Sequence;
 
+/**
+ * @psalm-immutable
+ */
 final class Failed
 {
     /**
diff --git a/src/Server/Process/Signaled.php b/src/Server/Process/Signaled.php
index 65f6d9d..953e02f 100644
--- a/src/Server/Process/Signaled.php
+++ b/src/Server/Process/Signaled.php
@@ -5,6 +5,9 @@
 
 use Innmind\Immutable\Sequence;
 
+/**
+ * @psalm-immutable
+ */
 final class Signaled
 {
     /**
diff --git a/src/Server/Process/Success.php b/src/Server/Process/Success.php
index 5644343..c89cbc3 100644
--- a/src/Server/Process/Success.php
+++ b/src/Server/Process/Success.php
@@ -5,6 +5,9 @@
 
 use Innmind\Immutable\Sequence;
 
+/**
+ * @psalm-immutable
+ */
 final class Success
 {
     /**
diff --git a/src/Server/Process/TimedOut.php b/src/Server/Process/TimedOut.php
index 042eb35..c49a6d2 100644
--- a/src/Server/Process/TimedOut.php
+++ b/src/Server/Process/TimedOut.php
@@ -5,6 +5,9 @@
 
 use Innmind\Immutable\Sequence;
 
+/**
+ * @psalm-immutable
+ */
 final class TimedOut
 {
     /**