Test for Trap::OutOfFuel instead of strings (#5297)

Update a few locations to test for a specific error code

Author: alexcrichton

crates/fuzzing/src/oracles.rs

@@ -306,13 +306,10 @@ pub fn instantiate_with_dummy(store: &mut Store<StoreLimits>, module: &Module) -
     }
 
     let string = e.to_string();
-    // Also allow errors related to fuel consumption
-    if string.contains("all fuel consumed")
-        // Currently we instantiate with a `Linker` which can't instantiate
-        // every single module under the sun due to using name-based resolution
-        // rather than positional-based resolution
-        || string.contains("incompatible import type")
-    {
+    // Currently we instantiate with a `Linker` which can't instantiate
+    // every single module under the sun due to using name-based resolution
+    // rather than positional-based resolution
+    if string.contains("incompatible import type") {
         log::debug!("failed to instantiate: {}", string);
         return None;
     }

tests/all/fuel.rs

@@ -116,11 +116,7 @@ fn iloop() {
         let mut store = Store::new(&engine, ());
         store.add_fuel(10_000).unwrap();
         let error = Instance::new(&mut store, &module, &[]).err().unwrap();
-        assert!(
-            format!("{:?}", error).contains("all fuel consumed"),
-            "bad error: {}",
-            error
-        );
+        assert_eq!(error.downcast::<Trap>().unwrap(), Trap::OutOfFuel);
     }
 }
 
@@ -172,10 +168,7 @@ fn host_function_consumes_all() {
     let instance = Instance::new(&mut store, &module, &[func.into()]).unwrap();
     let export = instance.get_typed_func::<(), ()>(&mut store, "").unwrap();
     let trap = export.call(&mut store, ()).unwrap_err();
-    assert!(
-        format!("{trap:?}").contains("all fuel consumed"),
-        "bad error: {trap:?}"
-    );
+    assert_eq!(trap.downcast::<Trap>().unwrap(), Trap::OutOfFuel);
 }
 
 #[test]