Add unit test to assert that calling Rust from PHP via FFI works

tests/Unit/RustFfiTest.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Tests\Unit;
+
+use Tests\UnitTestCase;
+
+class RustFfiTest extends UnitTestCase
+{
+    /**
+     * Test that we can call a Rust test program via PHP FFI.
+     */
+    public function testRustFfiInterface(): void
+    {
+        // Path to your .so file
+        $libPath = base_path('storage/ffi-libs/libtest_ffi.so');
+
+        // Define the function signature in C syntax
+        $ffi = \FFI::cdef("
+            char* rust_hello(void);
+        ", $libPath);
+
+        // Call the Rust function and get the returned string
+        /** @phpstan-ignore-next-line */
+        $result = $ffi->rust_hello();
+
+        // Convert the C string to a PHP string
+        $output = \FFI::string($result);
+
+        // Assert the expected output
+        $this->assertEquals("Hello from Rust!", $output);
+    }
+}