Add more tests

tests/compile-fail/used_underscore_binding.rs

@@ -2,22 +2,46 @@
 #![plugin(clippy)]
 #![deny(clippy)]
 
+/// Test that we lint if we use a binding with a single leading underscore
 fn prefix_underscore(_x: u32) -> u32 {
     _x + 1 //~ ERROR used binding which is prefixed with an underscore
 }
 
+/// Test that we lint even if the use is within a macro expansion
 fn in_macro(_x: u32) {
     println!("{}", _x); //~ ERROR used binding which is prefixed with an underscore
 }
 
+/// Test that we do not lint if the underscore is not a prefix
 fn non_prefix_underscore(some_foo: u32) -> u32 {
     some_foo + 1
 }
 
+/// Test that we do not lint if we do not use the binding
 fn unused_underscore(_foo: u32) -> u32 {
     1
 }
 
+// Non-variable bindings with preceding underscore
+fn _fn_test() {}
+struct _StructTest;
+enum _EnumTest {
+    _FieldA,
+    _FieldB(_StructTest)
+}
+
+/// Test that we do not lint for non-variable bindings
+fn non_variables() {
+    _fn_test();
+    let _s = _StructTest;
+    let _e = match _EnumTest::_FieldB(_StructTest) {
+        _EnumTest::_FieldA => 0,
+        _EnumTest::_FieldB(_st) => 1,
+    };
+    let f = _fn_test;
+    f();
+}
+
 fn main() {
     let foo = 0u32;
     // tests of unused_underscore lint
@@ -26,5 +50,6 @@ fn main() {
     // possible false positives
     let _ = non_prefix_underscore(foo);
     let _ = unused_underscore(foo);
+    non_variables();
 }