Add tests for duplicated attributes on expressions(#4452) (#4481)

* Add tests for duplicated attributes on expressions(#4452)

* Add necessary comments and fix the target

* Add comments for testings

* Fix testing for extra brace insertion

Author: chansuke

tests/source/issue-4475.rs

@@ -0,0 +1,4 @@
+fn main() {
+    #[cfg(debug_assertions)]
+    { println!("DEBUG"); }
+}

tests/target/issue-4452.rs

@@ -0,0 +1,19 @@
+fn a(&self) -> i64 {
+    // foo
+    #[allow(clippy::cast_possible_wrap)]
+    1u64 as i64
+}
+
+fn b(&self) -> i64 {
+    // bar
+    #[allow(clippy::cast_possible_wrap)]
+    #[attr]
+    1..2
+}
+
+fn foo() {
+    #[allow(clippy::cast_possible_wrap)]
+    {
+        // some comment
+    }
+}

tests/target/issue-4475.rs

@@ -0,0 +1,6 @@
+fn main() {
+    #[cfg(debug_assertions)]
+    {
+        println!("DEBUG");
+    }
+}