Add test for concat() after map()

Author: thekid

src/test/php/util/data/unittest/SequenceCreationTest.class.php

@@ -82,6 +82,14 @@ public function concat() {
     );
   }
 
+  #[Test]
+  public function concat_after_mapping() {
+    $this->assertSequence(
+      [2, 4, 6, 'EOF'],
+      Sequence::of([1, 2, 3])->map(fn($e) => $e * 2)->concat(['EOF'])
+    );
+  }
+
   #[Test, Expect(IllegalArgumentException::class)]
   public function cannot_concat_non_enumerable() {
     Sequence::$EMPTY->concat('test');