work around all test strings being static

compiler/builtins/bitcode/src/str.zig

@@ -1521,6 +1521,8 @@ pub fn strTrim(string: RocStr) callconv(.C) RocStr {
             return RocStr.init(string.asU8ptr() + leading_bytes, new_len);
         }
 
+        // nonempty, large, and unique:
+
         if (leading_bytes > 0) {
             var i: usize = 0;
             while (i < new_len) : (i += 1) {
@@ -1605,11 +1607,7 @@ const ReverseUtf8Iterator = struct {
             const cp_len = unicode.utf8ByteSequenceLength(it.bytes[i]) catch unreachable;
             const slice = it.bytes[i .. i + cp_len];
 
-            if (i == 0) {
+            it.i = if (i == 0) null else i - 1;
-                it.i = null;
-            } else {
-                it.i = i - 1;
-            }
 
             return slice;
         } else {

compiler/test_gen/src/gen_str.rs

@@ -984,7 +984,7 @@ fn str_trim_empty_string() {
 }
 
 #[test]
-fn str_trim_blank_string() {
+fn str_trim_small_blank_string() {
     assert_evals_to!(indoc!(r#"Str.trim " ""#), RocStr::from(""), RocStr);
 }
 
@@ -998,18 +998,18 @@ fn str_trim_small_to_small() {
 }
 
 #[test]
-fn str_trim_large_to_large() {
+fn str_trim_large_to_large_unique() {
     assert_evals_to!(
-        indoc!(r#"Str.trim "  hello giant world  ""#),
+        indoc!(r#"Str.trim (Str.concat "  " "hello world from a large string ")"#),
-        RocStr::from("hello giant world"),
+        RocStr::from("hello world from a large string"),
         RocStr
     );
 }
 
 #[test]
-fn str_trim_large_to_small() {
+fn str_trim_large_to_small_unique() {
     assert_evals_to!(
-        indoc!(r#"Str.trim "  hello world        ""#),
+        indoc!(r#"Str.trim (Str.concat "  " "hello world        ")"#),
         RocStr::from("hello world"),
         RocStr
     );