1 files changed, 51 insertions, 0 deletions
diff --git a/src/tools/clippy/tests/ui/explicit_write.rs b/src/tools/clippy/tests/ui/explicit_write.rs
new file mode 100644
index 00000000000..455c5ef55d0
--- /dev/null
+++ b/src/tools/clippy/tests/ui/explicit_write.rs
@@ -0,0 +1,51 @@
+// run-rustfix
+#![allow(unused_imports)]
+#![warn(clippy::explicit_write)]
+
+fn stdout() -> String {
+    String::new()
+}
+
+fn stderr() -> String {
+    String::new()
+}
+
+fn main() {
+    // these should warn
+    {
+        use std::io::Write;
+        write!(std::io::stdout(), "test").unwrap();
+        write!(std::io::stderr(), "test").unwrap();
+        writeln!(std::io::stdout(), "test").unwrap();
+        writeln!(std::io::stderr(), "test").unwrap();
+        std::io::stdout().write_fmt(format_args!("test")).unwrap();
+        std::io::stderr().write_fmt(format_args!("test")).unwrap();
+
+        // including newlines
+        writeln!(std::io::stdout(), "test\ntest").unwrap();
+        writeln!(std::io::stderr(), "test\ntest").unwrap();
+    }
+    // these should not warn, different destination
+    {
+        use std::fmt::Write;
+        let mut s = String::new();
+        write!(s, "test").unwrap();
+        write!(s, "test").unwrap();
+        writeln!(s, "test").unwrap();
+        writeln!(s, "test").unwrap();
+        s.write_fmt(format_args!("test")).unwrap();
+        s.write_fmt(format_args!("test")).unwrap();
+        write!(stdout(), "test").unwrap();
+        write!(stderr(), "test").unwrap();
+        writeln!(stdout(), "test").unwrap();
+        writeln!(stderr(), "test").unwrap();
+        stdout().write_fmt(format_args!("test")).unwrap();
+        stderr().write_fmt(format_args!("test")).unwrap();
+    }
+    // these should not warn, no unwrap
+    {
+        use std::io::Write;
+        std::io::stdout().write_fmt(format_args!("test")).expect("no stdout");
+        std::io::stderr().write_fmt(format_args!("test")).expect("no stderr");
+    }
+}