Make modules with tests runnable

Fixes #154

crates/ra_hir/src/module.rs

@@ -75,6 +75,11 @@ impl Module {
         Some(Crate::new(crate_id))
     }
 
+    /// Returns the all modulkes on the way to the root.
+    pub fn path_to_root(&self) -> Vec<Module> {
+        generate(Some(self.clone()), move |it| it.parent()).collect::<Vec<Module>>()
+    }
+
     /// The root of the tree this module is part of
     pub fn crate_root(&self) -> Module {
         let root_id = self.module_id.crate_root(&self.tree);