add test for str concat on non-unique first argument

crates/valgrind/src/lib.rs

@@ -41,6 +41,7 @@ fn valgrind_test_linux(source: &str) {
     for line in source.lines() {
         app_module_source.push_str("    ");
         app_module_source.push_str(line);
+        app_module_source.push('\n');
     }
 
     let temp_dir = tempfile::tempdir().unwrap();
@@ -68,6 +69,12 @@ fn valgrind_test_linux(source: &str) {
 
             run_with_valgrind(&binary_path);
         }
+        Err(roc_cli::build::BuildFileError::LoadingProblem(
+            roc_load::LoadingProblem::FormattedReport(report),
+        )) => {
+            eprintln!("{}", report);
+            panic!("");
+        }
         Err(e) => panic!("{:?}", e),
     }
 
@@ -178,3 +185,21 @@ fn split_not_present() {
         "#
     ));
 }
+
+#[test]
+fn str_concat_first_argument_not_unique() {
+    valgrind_test(indoc!(
+        r#"
+        (
+            str1 = Str.reserve "" 48
+            str2 = "a"
+
+            out = Str.concat str1 str2
+            if Bool.false then
+                out
+            else
+                str1
+            )
+        "#
+    ));
+}