Add ui test for write_and_append lint

Author: GuillaumeGomez

tests/ui/ineffective_open_options.fixed

@@ -0,0 +1,41 @@
+#![warn(clippy::ineffective_open_options)]
+
+use std::fs::OpenOptions;
+
+fn main() {
+    let file = OpenOptions::new()
+        .create(true)
+         //~ ERROR: unnecessary use of `.write(true)`
+        .append(true)
+        .open("dump.json")
+        .unwrap();
+
+    let file = OpenOptions::new()
+        .create(true)
+        .append(true)
+         //~ ERROR: unnecessary use of `.write(true)`
+        .open("dump.json")
+        .unwrap();
+
+    // All the next calls are ok.
+    let file = OpenOptions::new()
+        .create(true)
+        .write(false)
+        .append(true)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new()
+        .create(true)
+        .write(true)
+        .append(false)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new()
+        .create(true)
+        .write(false)
+        .append(false)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new().create(true).append(true).open("dump.json").unwrap();
+    let file = OpenOptions::new().create(true).write(true).open("dump.json").unwrap();
+}

tests/ui/ineffective_open_options.rs

@@ -0,0 +1,41 @@
+#![warn(clippy::ineffective_open_options)]
+
+use std::fs::OpenOptions;
+
+fn main() {
+    let file = OpenOptions::new()
+        .create(true)
+        .write(true) //~ ERROR: unnecessary use of `.write(true)`
+        .append(true)
+        .open("dump.json")
+        .unwrap();
+
+    let file = OpenOptions::new()
+        .create(true)
+        .append(true)
+        .write(true) //~ ERROR: unnecessary use of `.write(true)`
+        .open("dump.json")
+        .unwrap();
+
+    // All the next calls are ok.
+    let file = OpenOptions::new()
+        .create(true)
+        .write(false)
+        .append(true)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new()
+        .create(true)
+        .write(true)
+        .append(false)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new()
+        .create(true)
+        .write(false)
+        .append(false)
+        .open("dump.json")
+        .unwrap();
+    let file = OpenOptions::new().create(true).append(true).open("dump.json").unwrap();
+    let file = OpenOptions::new().create(true).write(true).open("dump.json").unwrap();
+}

tests/ui/ineffective_open_options.stderr

@@ -0,0 +1,17 @@
+error: unnecessary use of `.write(true)` because there is `.append(true)`
+  --> $DIR/ineffective_open_options.rs:8:9
+   |
+LL |         .write(true)
+   |         ^^^^^^^^^^^^ help: remove `.write(true)`
+   |
+   = note: `-D clippy::ineffective-open-options` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::ineffective_open_options)]`
+
+error: unnecessary use of `.write(true)` because there is `.append(true)`
+  --> $DIR/ineffective_open_options.rs:16:9
+   |
+LL |         .write(true)
+   |         ^^^^^^^^^^^^ help: remove `.write(true)`
+
+error: aborting due to 2 previous errors
+