internal: start new macro test suite

I don't like our macro tests -- they are brittle and don't inspire
confidence. I think the reason for that is that we try to unit-test
them, but that is at odds with reality, where macro expansion
fundamentally depends on name resolution.

crates/mbe/src/expander.rs

@@ -114,64 +114,3 @@ enum Fragment {
     /// like `$i * 2` where `$i = 1 + 1` work as expectd.
     Ast(tt::TokenTree),
 }
-
-#[cfg(test)]
-mod tests {
-    use syntax::{ast, AstNode};
-
-    use super::*;
-    use crate::syntax_node_to_token_tree;
-
-    #[test]
-    fn test_expand_rule() {
-        assert_err(
-            "($($i:ident);*) => ($i)",
-            "foo!{a}",
-            ExpandError::BindingError(String::from(
-                "expected simple binding, found nested binding `i`",
-            )),
-        );
-
-        // FIXME:
-        // Add an err test case for ($($i:ident)) => ($())
-    }
-
-    fn assert_err(macro_body: &str, invocation: &str, err: ExpandError) {
-        assert_eq!(
-            expand_first(&create_rules(&format_macro(macro_body)), invocation).err,
-            Some(err)
-        );
-    }
-
-    fn format_macro(macro_body: &str) -> String {
-        format!(
-            "
-        macro_rules! foo {{
-            {}
-        }}
-",
-            macro_body
-        )
-    }
-
-    fn create_rules(macro_definition: &str) -> crate::MacroRules {
-        let source_file = ast::SourceFile::parse(macro_definition).ok().unwrap();
-        let macro_definition =
-            source_file.syntax().descendants().find_map(ast::MacroRules::cast).unwrap();
-
-        let (definition_tt, _) =
-            syntax_node_to_token_tree(macro_definition.token_tree().unwrap().syntax());
-        crate::MacroRules::parse(&definition_tt).unwrap()
-    }
-
-    fn expand_first(rules: &crate::MacroRules, invocation: &str) -> ExpandResult<tt::Subtree> {
-        let source_file = ast::SourceFile::parse(invocation).ok().unwrap();
-        let macro_invocation =
-            source_file.syntax().descendants().find_map(ast::MacroCall::cast).unwrap();
-
-        let (invocation_tt, _) =
-            syntax_node_to_token_tree(macro_invocation.token_tree().unwrap().syntax());
-
-        expand_rules(&rules.rules, &invocation_tt)
-    }
-}