add unit test for result_map_unwrap_or

Author: Guanqun Lu

tests/ui/result_map_unwrap_or.rs

@@ -0,0 +1,14 @@
+#![warn(clippy::result_map_unwrap_or)]
+
+fn main() {
+    let res: Result<usize, ()> = Ok(1);
+
+    // Check `RESULT_MAP_OR_NONE`.
+    // Single line case.
+    let _ = res.map(|x| x + 1).unwrap_or(0);
+    // Multi-line case.
+    #[rustfmt::skip]
+    let _ = res.map(|x| {
+                        x + 1
+                       }).unwrap_or(0);
+}

tests/ui/result_map_unwrap_or.stderr

@@ -0,0 +1,20 @@
+error: called `map(f).unwrap_or(a)` on a Result value. This can be done more directly by calling `map_or(a, f)` instead
+  --> $DIR/result_map_unwrap_or.rs:8:13
+   |
+LL |     let _ = res.map(|x| x + 1).unwrap_or(0);
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::result-map-unwrap-or` implied by `-D warnings`
+   = note: replace `map(|x| x + 1).unwrap_or(0)` with `map_or(0, |x| x + 1)`
+
+error: called `map(f).unwrap_or(a)` on a Result value. This can be done more directly by calling `map_or(a, f)` instead
+  --> $DIR/result_map_unwrap_or.rs:11:13
+   |
+LL |       let _ = res.map(|x| {
+   |  _____________^
+LL | |                         x + 1
+LL | |                        }).unwrap_or(0);
+   | |______________________________________^
+
+error: aborting due to 2 previous errors
+