Add failing test for #3778 write_with_newline

Literal `\n` characters (not a newline) in a `r"raw"` string should not
fail the lint.

diff --git a/tests/ui/write_with_newline.rs b/tests/ui/write_with_newline.rs
index 2f53d4561af8ceda2b01a1c01d8cdf81a052093b..02e043f9233e0ffc6a64dc1060cec1bdba8a0811 100644 (file)
--- a/tests/ui/write_with_newline.rs
+++ b/tests/ui/write_with_newline.rs
@@ -31,4 +31,7 @@ fn main() {
     write!(&mut v, "\\n"); // #3514
     write!(&mut v, "\\\n");
     write!(&mut v, "\\\\n");
+
+    // Raw strings
+    write!(&mut v, r"\n"); // #3778
 }