refactor/uucore ~ correct implementation of executable!() for multicall

- Use an atomic bool to track whether the utility name is the second
or the first argument.
- Add tests

tests/test_util_name.rs

@@ -0,0 +1,81 @@
+mod common;
+
+use common::util::TestScenario;
+
+#[test]
+#[cfg(feature = "ls")]
+fn execution_phrase_double() {
+    use std::process::Command;
+
+    let scenario = TestScenario::new("ls");
+    let output = Command::new(&scenario.bin_path)
+        .arg("ls")
+        .arg("--some-invalid-arg")
+        .output()
+        .unwrap();
+    assert!(String::from_utf8(output.stderr)
+        .unwrap()
+        .contains(&format!("USAGE:\n    {} ls", scenario.bin_path.display(),)));
+}
+
+#[test]
+#[cfg(feature = "ls")]
+fn execution_phrase_single() {
+    use std::process::Command;
+
+    let scenario = TestScenario::new("ls");
+    std::fs::copy(scenario.bin_path, scenario.fixtures.plus("uu-ls")).unwrap();
+    let output = Command::new(scenario.fixtures.plus("uu-ls"))
+        .arg("--some-invalid-arg")
+        .output()
+        .unwrap();
+    assert!(String::from_utf8(output.stderr).unwrap().contains(&format!(
+        "USAGE:\n    {}",
+        scenario.fixtures.plus("uu-ls").display()
+    )));
+}
+
+#[test]
+#[cfg(feature = "sort")]
+fn util_name_double() {
+    use std::{
+        io::Write,
+        process::{Command, Stdio},
+    };
+
+    let scenario = TestScenario::new("sort");
+    let mut child = Command::new(&scenario.bin_path)
+        .arg("sort")
+        .stdin(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .unwrap();
+    // input invalid utf8 to cause an error
+    child.stdin.take().unwrap().write_all(&[255]).unwrap();
+    let output = child.wait_with_output().unwrap();
+    assert!(String::from_utf8(output.stderr).unwrap().contains("sort: "));
+}
+
+#[test]
+#[cfg(feature = "sort")]
+fn util_name_single() {
+    use std::{
+        io::Write,
+        process::{Command, Stdio},
+    };
+
+    let scenario = TestScenario::new("sort");
+    std::fs::copy(scenario.bin_path, scenario.fixtures.plus("uu-sort")).unwrap();
+    let mut child = Command::new(scenario.fixtures.plus("uu-sort"))
+        .stdin(Stdio::piped())
+        .stderr(Stdio::piped())
+        .spawn()
+        .unwrap();
+    // input invalid utf8 to cause an error
+    child.stdin.take().unwrap().write_all(&[255]).unwrap();
+    let output = child.wait_with_output().unwrap();
+    assert!(String::from_utf8(output.stderr).unwrap().contains(&format!(
+        "{}: ",
+        scenario.fixtures.plus("uu-sort").display()
+    )));
+}