Revert "Use cargo-fmt in self_tests"

This reverts commit c63d42e804.

src/test/mod.rs

@@ -375,21 +375,43 @@ fn idempotence_tests() {
     });
 }
 
+// Run rustfmt on itself. This operation must be idempotent. We also check that
+// no warnings are emitted.
+// Issue-3443: these tests require nightly
 #[nightly_only_test]
 #[test]
 fn self_tests() {
-    let get_exe_path = |name| {
-        let mut path = env::current_exe().unwrap();
-        path.pop();
-        path.set_file_name(format!("{name}{}", env::consts::EXE_SUFFIX));
-        path
-    };
-    let status = Command::new(get_exe_path("cargo-fmt"))
-        .args(["--check", "--all"])
-        .env("RUSTFMT", get_exe_path("rustfmt"))
-        .status()
-        .unwrap();
-    assert!(status.success());
+    init_log();
+    let mut files = get_test_files(Path::new("tests"), false);
+    let bin_directories = vec!["cargo-fmt", "git-rustfmt", "bin", "format-diff"];
+    for dir in bin_directories {
+        let mut path = PathBuf::from("src");
+        path.push(dir);
+        path.push("main.rs");
+        files.push(path);
+    }
+    files.push(PathBuf::from("src/lib.rs"));
+
+    let (reports, count, fails) = check_files(files, &Some(PathBuf::from("rustfmt.toml")));
+    let mut warnings = 0;
+
+    // Display results.
+    println!("Ran {} self tests.", count);
+    assert_eq!(fails, 0, "{} self tests failed", fails);
+
+    for format_report in reports {
+        println!(
+            "{}",
+            FormatReportFormatterBuilder::new(&format_report).build()
+        );
+        warnings += format_report.warning_count();
+    }
+
+    assert_eq!(
+        warnings, 0,
+        "Rustfmt's code generated {} warnings",
+        warnings
+    );
 }
 
 #[test]