chore: add fmt test for validator

crates/aiken-lang/src/tests/format.rs

@@ -55,6 +55,27 @@ fn test_format_if() {
     assert_fmt(src, expected)
 }
 
+#[test]
+fn test_format_validator() {
+    let src = indoc! {r#"
+      validator foo ( ) {
+      fn(d: Datum, r: Redeemer, ctx: ScriptContext) -> Bool {
+      True
+      }
+      }
+    "#};
+
+    let expected = indoc! {r#"
+      validator foo {
+        fn(d: Datum, r: Redeemer, ctx: ScriptContext) -> Bool {
+          True
+        }
+      }
+    "#};
+
+    assert_fmt(src, expected)
+}
+
 #[test]
 fn test_format_when() {
     let src = indoc! {r#"