test(diagnostics): require accurate causes and source lines

Check native and IR rejection without creating or replacing output files.
Keep nine missing-location failures visible rather than accepting them.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

3 files changed, 17 insertions, 0 deletions

diff --git a/tests/iii/function-byref/case.json b/tests/iii/function-byref/case.json
new file mode 100644
index 0000000..e879655
--- /dev/null
+++ b/tests/iii/function-byref/case.json
@@ -0,0 +1,8 @@
+{
+  "errors": [
+    {
+      "reason": "BYREF\\ parameters\\ are\\ not\\ allowed\\ in\\ a\\ FUNCTION",
+      "line": 2
+    }
+  ]
+}
diff --git a/tests/iii/function-byref/notes.md b/tests/iii/function-byref/notes.md
new file mode 100644
index 0000000..4063bff
--- /dev/null
+++ b/tests/iii/function-byref/notes.md
@@ -0,0 +1,5 @@
+# function-byref
+
+CIE p. 24 explicitly prohibits passing function parameters by reference.
+
+Require exit 1, the stated cause and source line on the same diagnostic, exactly one compilation termination line, and preservation of absent/existing outputs for both native and IR requests. Missing block delimiters are located at EOF (the line after the final newline).
diff --git a/tests/iii/function-byref/program.cps b/tests/iii/function-byref/program.cps
new file mode 100644
index 0000000..1cc89cb
--- /dev/null
+++ b/tests/iii/function-byref/program.cps
@@ -0,0 +1,4 @@
+// BYREF is procedure-only.
+FUNCTION Bad(BYREF X : INTEGER) RETURNS INTEGER
+    RETURN X
+ENDFUNCTION