tests: add tests for assoscaited_type_bounds fix

tests/source/associated_type_bounds.rs

@@ -0,0 +1,13 @@
+// See #3657 - https://github.com/rust-lang/rustfmt/issues/3657
+
+#![feature(associated_type_bounds)]
+
+fn f<I: Iterator<Item: Clone>>() {}
+
+fn g<I: Iterator<Item : Clone>>() {}
+
+fn h<I: Iterator<Item :      Clone>>() {}
+
+fn i<I: Iterator<Item:Clone>>() {}
+
+fn j<I: Iterator<Item :  Clone+'a>>() {}

tests/target/associated_type_bounds.rs

@@ -0,0 +1,13 @@
+// See #3657 - https://github.com/rust-lang/rustfmt/issues/3657
+
+#![feature(associated_type_bounds)]
+
+fn f<I: Iterator<Item: Clone>>() {}
+
+fn g<I: Iterator<Item: Clone>>() {}
+
+fn h<I: Iterator<Item: Clone>>() {}
+
+fn i<I: Iterator<Item: Clone>>() {}
+
+fn j<I: Iterator<Item: Clone + 'a>>() {}