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diff --git a/src/test/ui/run-pass/macros/macro-comma-behavior.rs b/src/test/ui/run-pass/macros/macro-comma-behavior.rs
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+++ b/src/test/ui/run-pass/macros/macro-comma-behavior.rs
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+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Ideally, any macro call with a trailing comma should behave
+// identically to a call without the comma.
+//
+// This checks the behavior of macros with trailing commas in key
+// places where regressions in behavior seem highly possible (due
+// to it being e.g. a place where the addition of an argument
+// causes it to go down a code path with subtly different behavior).
+//
+// There is a companion test in compile-fail.
+
+// compile-flags: --test -C debug_assertions=yes
+// revisions: std core
+
+#![cfg_attr(core, no_std)]
+
+#[cfg(std)] use std::fmt;
+#[cfg(core)] use core::fmt;
+
+// an easy mistake in the implementation of 'assert!'
+// would cause this to say "explicit panic"
+#[test]
+#[should_panic(expected = "assertion failed")]
+fn assert_1arg() {
+    assert!(false,);
+}
+
+// same as 'assert_1arg'
+#[test]
+#[should_panic(expected = "assertion failed")]
+fn debug_assert_1arg() {
+    debug_assert!(false,);
+}
+
+// make sure we don't accidentally forward to `write!("text")`
+#[cfg(std)]
+#[test]
+fn writeln_1arg() {
+    use fmt::Write;
+
+    let mut s = String::new();
+    writeln!(&mut s,).unwrap();
+    assert_eq!(&s, "\n");
+}
+
+// A number of format_args-like macros have special-case treatment
+// for a single message string, which is not formatted.
+//
+// This test ensures that the addition of a trailing comma does not
+// suddenly cause these strings to get formatted when they otherwise
+// would not be. This is an easy mistake to make by having such a macro
+// accept ", $($tok:tt)*" instead of ", $($tok:tt)+" after its minimal
+// set of arguments.
+//
+// (Example: Issue #48042)
+#[test]
+fn to_format_or_not_to_format() {
+    // ("{}" is the easiest string to test because if this gets
+    // sent to format_args!, it'll simply fail to compile.
+    // "{{}}" is an example of an input that could compile and
+    // produce an incorrect program, but testing the panics
+    // would be burdensome.)
+    let falsum = || false;
+
+    assert!(true, "{}",);
+
+    // assert_eq!(1, 1, "{}",); // see compile-fail
+    // assert_ne!(1, 2, "{}",); // see compile-fail
+
+    debug_assert!(true, "{}",);
+
+    // debug_assert_eq!(1, 1, "{}",); // see compile-fail
+    // debug_assert_ne!(1, 2, "{}",); // see compile-fail
+    // eprint!("{}",); // see compile-fail
+    // eprintln!("{}",); // see compile-fail
+    // format!("{}",); // see compile-fail
+    // format_args!("{}",); // see compile-fail
+
+    if falsum() { panic!("{}",); }
+
+    // print!("{}",); // see compile-fail
+    // println!("{}",); // see compile-fail
+    // unimplemented!("{}",); // see compile-fail
+
+    if falsum() { unreachable!("{}",); }
+
+    // write!(&mut stdout, "{}",); // see compile-fail
+    // writeln!(&mut stdout, "{}",); // see compile-fail
+}