feat: let should_fail_with check that the failure reason contains the expected message (#5319)

# Description

## Problem

Resolves #4786

## Summary

`#[test(should_fail_with = "message")]` will now check that "message" is
a substring of the failure reason. I _think_ this is a
backwards-compatible change.

I thought about supporting regular expressions, as suggested in the
related issue, but I didn't know how to signal that it's a regex or just
"contains". I guess that could be done with another name, something like
`should_with_with_regexp` 🤔 (in a separate PR, if really needed/wanted)

## Additional Context

None

## Documentation

Check one:
- [ ] No documentation needed.
- [x] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

Author: asterite

docs/docs/tooling/testing.md

@@ -42,7 +42,7 @@ fn test_add() {
 }
 ```
 
-You can be more specific and make it fail with a specific reason by using `should_fail_with = "<the reason for failure>`:
+You can be more specific and make it fail with a specific reason by using `should_fail_with = "<the reason for failure>"`:
 
 ```rust
 fn main(african_swallow_avg_speed : Field) {
@@ -58,5 +58,22 @@ fn test_king_arthur() {
 fn test_bridgekeeper() {
     main(32);
 }
-
 ```
+
+The string given to `should_fail_with` doesn't need to exactly match the failure reason, it just needs to be a substring of it:
+
+```rust
+fn main(african_swallow_avg_speed : Field) {
+    assert(african_swallow_avg_speed == 65, "What is the airspeed velocity of an unladen swallow");
+}
+
+#[test]
+fn test_king_arthur() {
+    main(65);
+}
+
+#[test(should_fail_with = "airspeed velocity")]
+fn test_bridgekeeper() {
+    main(32);
+}
+```

test_programs/noir_test_failure/should_fail_mismatch/src/main.nr

@@ -2,14 +2,9 @@
 fn test_different_string() {
     assert_eq(0, 1, "Different string");
 }
-// The assert message has a space
-#[test(should_fail_with = "Not equal")]
-fn test_with_extra_space() {
-    assert_eq(0, 1, "Not equal ");
-}
-// The assert message has a space
-#[test(should_fail_with = "Not equal")]
-fn test_runtime_mismatch() {
-    // We use a pedersen commitment here so that the assertion failure is only known at runtime.
-    assert_eq(std::hash::pedersen_commitment([27]).x, 0, "Not equal ");
-}
+
+// The failure reason is a substring of the expected message, but it should be the other way around
+#[test(should_fail_with = "Definitely Not equal!")]
+fn test_wrong_expectation() {
+    assert_eq(0, 1, "Not equal");
+}

test_programs/noir_test_success/should_fail_with_matches/src/main.nr

@@ -3,6 +3,11 @@ fn test_should_fail_with_match() {
     assert_eq(0, 1, "Not equal");
 }
 
+#[test(should_fail_with = "Not equal")]
+fn test_should_fail_with_match_partial_match() {
+    assert_eq(0, 1, "Definitely Not equal!");
+}
+
 #[test(should_fail)]
 fn test_should_fail_without_match() {
     assert_eq(0, 1);
@@ -48,6 +53,11 @@ unconstrained fn unconstrained_test_should_fail_with_match() {
     assert_eq(0, 1, "Not equal");
 }
 
+#[test(should_fail_with = "Not equal")]
+unconstrained fn unconstrained_test_should_fail_with_match_partial_match() {
+    assert_eq(0, 1, "Definitely Not equal!");
+}
+
 #[test(should_fail)]
 unconstrained fn unconstrained_test_should_fail_without_match() {
     assert_eq(0, 1);

tooling/nargo/src/ops/test.rs

@@ -128,7 +128,7 @@ fn check_expected_failure_message(
     };
 
     let expected_failure_message_matches =
-        matches!(&failed_assertion, Some(message) if message == expected_failure_message);
+        matches!(&failed_assertion, Some(message) if message.contains(expected_failure_message));
     if expected_failure_message_matches {
         return TestStatus::Pass;
     }