add test

Author: karolzwolak

tests/ui/lint/default-groups-issue-65464.rs

@@ -0,0 +1,14 @@
+//@ check-pass
+
+// Verify information about membership to builtin lint group is included in the lint message when
+// explaining lint level and source for builtin lints with default settings.
+//
+// Ideally, we'd like to use lints that are part of `unused` group as shown in the issue.
+// This is not possible in an ui test, because `unused` lints are enabled with `-A unused`
+// in such tests, and the we're testing a scenario with no modification to the default settings.
+
+fn main() {
+    let WrongCase = 1;
+    //~^ WARN [non_snake_case]
+    //~| NOTE `#[warn(non_snake_case)]` (part of `#[warn(nonstandard_style)]`) on by default
+}

tests/ui/lint/default-groups-issue-65464.stderr

@@ -0,0 +1,10 @@
+warning: variable `WrongCase` should have a snake case name
+  --> $DIR/default-groups-issue-65464.rs:11:9
+   |
+LL |     let WrongCase = 1;
+   |         ^^^^^^^^^ help: convert the identifier to snake case: `wrong_case`
+   |
+   = note: `#[warn(non_snake_case)]` (part of `#[warn(nonstandard_style)]`) on by default
+
+warning: 1 warning emitted
+