message: Use .join on slice over iter().join where we can
  Summary: If the input is [String], we can use the method directly on slice, so do that instead.
diff: @@ -66,7 +66,7 @@ impl ConformanceTest {
  .collect::<Vec<_>>()
  .split(|x| *x == "---")
  .map(|xs| Self {
  - code: xs.iter().join("\n"),
  + code: xs.join("\n"),
  error: xs
  .iter()
  .find_position(|x| x.contains("###"))
  