more test cleanup

kiln-core/src/tile.rs

@@ -135,11 +135,17 @@ impl ScriptKey {
         }
     }
 
-    pub fn source<'a>(&self, sources: &'a HashMap<String, String>) -> Option<&'a str> {
+    /// Attempt to find and return the source for the given script key:
+    /// - For `None`, return Ok(None) since there's not a script to find
+    /// - For `World`, return either Ok(Some(&str)) or Err if it's not in the given hashmap
+    /// - For `Builtin`, return Ok(Some(&str)) assuming the builtin is a valid name (Err in the unlikely case...)
+    pub fn source<'a>(&self, sources: &'a HashMap<String, String>) -> Result<Option<&'a str>, String> {
         match self {
-            ScriptKey::None => None,
-            ScriptKey::World(name) => sources.get(name).map(String::as_str),
-            key @ ScriptKey::Builtin(_) => BUILTIN_SOURCES.get(key).copied(),
+            ScriptKey::None => Ok(None),
+            ScriptKey::World(name) => sources.get(name).map(String::as_str)
+                .map_or(Err(format!("unknown script '{name}'")), |s| Ok(Some(s))),
+            key @ ScriptKey::Builtin(name) => BUILTIN_SOURCES.get(key)
+                .map_or(Err(format!("No builtin script '{name}'")), |s| Ok(Some(*s))),
         }
     }
 }