Consistent underscores in root directory

test_suite/tests/compile-fail/unknown-attribute/container.rs

@@ -0,0 +1,10 @@
+#[macro_use]
+extern crate serde_derive;
+
+#[derive(Serialize)] //~ ERROR: custom derive attribute panicked
+#[serde(abc="xyz")] //~^ HELP: unknown serde container attribute `abc`
+struct A {
+    x: u32,
+}
+
+fn main() { }

test_suite/tests/compile-fail/unknown-attribute/field.rs

@@ -0,0 +1,10 @@
+#[macro_use]
+extern crate serde_derive;
+
+#[derive(Serialize)] //~ ERROR: custom derive attribute panicked
+struct C {
+    #[serde(abc="xyz")] //~^^ HELP: unknown serde field attribute `abc`
+    x: u32,
+}
+
+fn main() { }

test_suite/tests/compile-fail/unknown-attribute/variant.rs

@@ -0,0 +1,10 @@
+#[macro_use]
+extern crate serde_derive;
+
+#[derive(Serialize)] //~ ERROR: custom derive attribute panicked
+enum E {
+    #[serde(abc="xyz")] //~^^ HELP: unknown serde variant attribute `abc`
+    V,
+}
+
+fn main() { }