Fix tests.

tests/constants.rs

@@ -87,7 +87,7 @@ fn test_constant_mut() -> Result<(), Box<EvalAltResult>> {
                 "
             )
             .expect_err("should error"),
-        EvalAltResult::ErrorAssignmentToConstant(..)
+        EvalAltResult::ErrorNonPureMethodCallOnConstant(..)
     ));
 
     let mut scope = Scope::new();
@@ -120,7 +120,7 @@ fn test_constant_mut() -> Result<(), Box<EvalAltResult>> {
         *engine
             .run_with_scope(&mut scope, "MY_NUMBER.value = 42;")
             .expect_err("should error"),
-        EvalAltResult::ErrorAssignmentToConstant(..)
+        EvalAltResult::ErrorNonPureMethodCallOnConstant(..)
     ));
 
     Ok(())

tests/plugins.rs

@@ -119,7 +119,7 @@ fn test_plugins_package() -> Result<(), Box<EvalAltResult>> {
 
         assert!(
             matches!(*engine.run("const A = [1, 2, 3]; A.test(42);").expect_err("should error"),
-            EvalAltResult::ErrorAssignmentToConstant(x, ..) if x == "array")
+            EvalAltResult::ErrorNonPureMethodCallOnConstant(x, ..) if x == "test")
         )
     }