add test cases for #12435

Author: J-ZhengLi

tests/ui/mixed_attributes_style.rs

@@ -38,3 +38,18 @@ mod bar {
 fn main() {
     // test code goes here
 }
+
+// issue #12435
+#[cfg(test)]
+mod tests {
+    //! Module doc, don't lint
+}
+#[allow(unused)]
+mod baz {
+    //! Module doc, don't lint
+    const FOO: u8 = 0;
+}
+/// Module doc, don't lint
+mod quz {
+    #![allow(unused)]
+}

tests/ui/mixed_attributes_style.stderr

@@ -26,5 +26,29 @@ LL | | mod bar {
 LL | |     #![allow(unused)]
    | |_____________________^
 
-error: aborting due to 3 previous errors
+error: item has both inner and outer attributes
+  --> tests/ui/mixed_attributes_style.rs:43:1
+   |
+LL | / #[cfg(test)]
+LL | | mod tests {
+LL | |     //! Module doc, don't lint
+   | |______________________________^
+
+error: item has both inner and outer attributes
+  --> tests/ui/mixed_attributes_style.rs:47:1
+   |
+LL | / #[allow(unused)]
+LL | | mod baz {
+LL | |     //! Module doc, don't lint
+   | |______________________________^
+
+error: item has both inner and outer attributes
+  --> tests/ui/mixed_attributes_style.rs:52:1
+   |
+LL | / /// Module doc, don't lint
+LL | | mod quz {
+LL | |     #![allow(unused)]
+   | |_____________________^
+
+error: aborting due to 6 previous errors