test(tvix/eval): Add proof-of-concept test for Chunk

This is pretty boring at the moment, but mostly serves as a foot in the
door in the direction of writing more tests

Change-Id: Id88eb4ec7e53ebb2d5b5c254c8f45ff750238811
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6637
Autosubmit: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/eval/src/test_utils.rs

@@ -0,0 +1,8 @@
+use codemap::CodeMap;
+
+/// Create a dummy [`codemap::Span`] for use in tests
+pub(crate) fn dummy_span() -> codemap::Span {
+    let mut codemap = CodeMap::new();
+    let file = codemap.add_file("<dummy>".to_owned(), "<dummy>".to_owned());
+    file.span
+}