non-working version

app/FooDecorator.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace App;
+
+class FooDecorator implements FooContract
+{
+    public function __construct(private FooContract $parent)
+    {}
+
+    public function bar(): string
+    {
+        return strrev($this->parent->bar());
+    }
+}

app/Providers/AppServiceProvider.php

@@ -4,6 +4,7 @@
 
 use App\Foo;
 use App\FooContract;
+use App\FooDecorator;
 use Illuminate\Support\ServiceProvider;
 
 class AppServiceProvider extends ServiceProvider
@@ -15,7 +16,13 @@ class AppServiceProvider extends ServiceProvider
      */
     public function register()
     {
-        $this->app->bind(FooContract::class, Foo::class);
+        $this->app->bind(FooContract::class, fn () => new Foo('any'));
+
+        $decorator = new FooDecorator(
+            $this->app->make(FooContract::class)
+        );
+
+        $this->app->instance(FooContract::class, $decorator);
     }
 
     /**

composer.json

@@ -5,7 +5,7 @@
     "keywords": ["framework", "laravel"],
     "license": "MIT",
     "require": {
-        "php": "^7.3|^8.0",
+        "php": "8.0",
         "fideloper/proxy": "^4.4",
         "fruitcake/laravel-cors": "^2.0",
         "guzzlehttp/guzzle": "^7.0.1",

tests/Unit/ExampleTest.php

@@ -8,35 +8,17 @@
 
 class ExampleTest extends TestCase
 {
-    public function testFoo1()
-    {
-        // Works as expected
-        $result = resolve(FooContract::class, ['baz' => 'baz'])->bar(); // "qux"
-
-        $this->assertEquals('qux', $result);
-    }
-
     public function testFoo2()
     {
-        // Would expect to get "corge"...
-        $this->mock(FooContract::class, function (MockInterface $mock) {
-            $mock->shouldReceive('bar')->once()->andReturn('corge');
-        });
-
-        $result = resolve(FooContract::class, ['baz' => 'baz'])->bar(); // ... but still getting "qux"
+        $result = resolve(FooContract::class, ['baz' => 'baz'])->bar();
 
-        $this->assertEquals('corge', $result);
+        $this->assertEquals('xuq', $result);
     }
 
     public function testFoo3()
     {
-        $this->mock(FooContract::class, function (MockInterface $mock) {
-            $mock->shouldReceive('bar')->once()->andReturn('corge');
-        });
-
-        // I just remove the constructor arguments...
-        $result = resolve(FooContract::class)->bar(); // ... and I now get "corge" as expected
+        $result = resolve(FooContract::class)->bar();
 
-        $this->assertEquals('corge', $result);
+        $this->assertEquals('xuq', $result);
     }
 }