fix(tvix/eval): restore .exp.xml files and skip in test suite

Change-Id: Iebda5e0d99925a0a8c1d6ae1d7a35397d127bf31
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7047
Autosubmit: sterni <sternenseemann@systemli.org>
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/eval/src/tests/mod.rs

@@ -9,9 +9,16 @@ fn eval_test(code_path: &str, expect_success: bool) {
         .strip_suffix("nix")
         .expect("test files always end in .nix");
     let exp_path = format!("{}exp", base);
+    let exp_xml_path = std::path::PathBuf::from(format!("{}exp.xml", base));
 
     let code = std::fs::read_to_string(code_path).expect("should be able to read test code");
 
+    if exp_xml_path.exists() {
+        // We can't test them at the moment because we don't have XML output yet.
+        // Checking for success / failure only is a bit disingenious.
+        return;
+    }
+
     match interpret(&code, Some(code_path.into()), Options::test_options()) {
         Ok(result) => {
             let result_str = format!("{}", result);