Verify missing argument

Author: thekid

src/test/php/lang/ast/unittest/emit/PipelinesTest.class.php

@@ -110,14 +110,23 @@ public function run() {
   }
 
   #[Test, Expect(Error::class)]
-  public function pipe_to_missing() {
+  public function missing_function() {
     $this->run('class %T {
       public function run() {
         return "test" |> "__missing";
       }
     }');
   }
 
+  #[Test, Expect(Error::class)]
+  public function missing_argument() {
+    $this->run('class %T {
+      public function run() {
+        return 5 |> fn($a, $b) => $a * $b;
+      }
+    }');
+  }
+
   #[Test]
   public function pipe_chain() {
     $r= $this->run('class %T {