tests: add test for s.$method() with T.methods (#8451)

vlib/v/tests/comptime_call_test.v

@@ -1,7 +1,7 @@
 struct Test {}
 
 fn (test Test) v() {
-	println('in v()')
+	println('Test.v()')
 }
 fn (test Test) i() int {
 	return 4
@@ -13,7 +13,7 @@ fn (test Test) s2() string {
 	return 'Two'
 }
 
-fn test_call() {
+fn test_string_identifier() {
 	test := Test{}
 	sv := 'v'
 	test.$sv()
@@ -24,3 +24,29 @@ fn test_call() {
 	rs := test.$ss()
 	assert rs == 'test'
 }
+
+fn test_for_methods() {
+	test := Test{}
+	mut r := ''
+	$for method in Test.methods {
+		// currently the checker thinks all $method calls return string
+		$if method.return_type is string {
+			//~ $if method.name == 's' {println('yes')}
+			v := test.$method()
+			r += v.str()
+		}
+		$else $if method.return_type is int {
+			// TODO
+			//v := test.$method()
+			v := '?'
+			r += v.str()
+			assert method.name == 'i'
+		}
+		$else {
+			// no return type
+			test.$method()
+			assert method.name == 'v'
+		}
+	}
+	assert r == '?testTwo'
+}