tabify tests (#3220)

* tabify tests

* move mod tests; up

polkadot/node/collation-generation/src/lib.rs

@@ -49,6 +49,9 @@ use std::sync::Arc;
 
 mod error;
 
+#[cfg(test)]
+mod tests;
+
 const LOG_TARGET: &'static str = "parachain::collation-generation";
 
 /// Collation Generation Subsystem
@@ -506,6 +509,3 @@ impl metrics::Metrics for Metrics {
 		Ok(Metrics(Some(metrics)))
 	}
 }
-
-#[cfg(test)]
-mod tests;