Add tests for unsized trait in wrong_self_convention lint

tests/ui/use_self.fixed

@@ -71,7 +71,7 @@ mod lifetimes {
 
 mod issue2894 {
     trait IntoBytes {
-        #[allow(clippy::clippy::wrong_self_convention)]
+        #[allow(clippy::wrong_self_convention)]
         fn into_bytes(&self) -> Vec<u8>;
     }
 

tests/ui/wrong_self_convention.rs

@@ -113,4 +113,27 @@ mod issue6307 {
         fn from_(self) {}
         fn to_mut(&mut self) {}
     }
+
+    trait U {
+        fn as_i32(self);
+        fn as_u32(&self);
+        fn into_i32(&self);
+        fn into_u32(self);
+        fn is_i32(self);
+        fn is_u32(&self);
+        fn to_i32(self);
+        fn to_u32(&self);
+        fn from_i32(self);
+        // check whether the lint can be allowed at the function level
+        #[allow(clippy::wrong_self_convention)]
+        fn from_cake(self);
+
+        // test for false positives
+        fn as_(self);
+        fn into_(&self);
+        fn is_(self);
+        fn to_(self);
+        fn from_(self);
+        fn to_mut(&mut self);
+    }
 }

tests/ui/wrong_self_convention.stderr

@@ -102,5 +102,35 @@ error: methods called `from_*` usually take no self; consider choosing a less am
 LL |         fn from_i32(self) {}
    |                     ^^^^
 
-error: aborting due to 17 previous errors
+error: methods called `as_*` usually take self by reference or self by mutable reference; consider choosing a less ambiguous name
+  --> $DIR/wrong_self_convention.rs:118:19
+   |
+LL |         fn as_i32(self);
+   |                   ^^^^
+
+error: methods called `into_*` usually take self by value; consider choosing a less ambiguous name
+  --> $DIR/wrong_self_convention.rs:120:21
+   |
+LL |         fn into_i32(&self);
+   |                     ^^^^^
+
+error: methods called `is_*` usually take self by reference or no self; consider choosing a less ambiguous name
+  --> $DIR/wrong_self_convention.rs:122:19
+   |
+LL |         fn is_i32(self);
+   |                   ^^^^
+
+error: methods called `to_*` usually take self by reference; consider choosing a less ambiguous name
+  --> $DIR/wrong_self_convention.rs:124:19
+   |
+LL |         fn to_i32(self);
+   |                   ^^^^
+
+error: methods called `from_*` usually take no self; consider choosing a less ambiguous name
+  --> $DIR/wrong_self_convention.rs:126:21
+   |
+LL |         fn from_i32(self);
+   |                     ^^^^
+
+error: aborting due to 22 previous errors