Add explicit --cargo-test-arg option for test arguments

Co-authored-by: sourcefrog <346355+sourcefrog@users.noreply.github.com>

Author: Copilot

book/src/cargo-args.md

@@ -56,12 +56,26 @@ excludes doctests. (If the doctests are numerous and slow, and not relied upon t
 cargo mutants -- --all-targets
 ```
 
+Alternatively, you can use the explicit `--cargo-test-arg` option, which can be repeated:
+
+```shell
+cargo mutants --cargo-test-arg=--all-targets --cargo-test-arg=--no-fail-fast
+```
+
+Both formats can be used together if needed:
+
+```shell
+cargo mutants --cargo-test-arg=--all-targets -- --nocapture
+```
+
 These options can also be configured statically with the `additional_cargo_test_args` key in `.cargo/mutants.toml`:
 
 ```toml
 additional_cargo_test_args = ["--jobs=1"]
 ```
 
+When both command-line options and configuration are specified, arguments from `--cargo-test-arg`, then arguments after `--`, and finally configuration file arguments are all combined in that order.
+
 ## Arguments to test binaries
 
 You can use a second double-dash to pass options through to the test targets:

src/main.rs

@@ -220,6 +220,10 @@ pub struct Args {
     )]
     cargo_arg: Vec<String>,
 
+    /// Additional args for cargo test.
+    #[arg(long, allow_hyphen_values = true, help_heading = "Execution")]
+    cargo_test_arg: Vec<String>,
+
     /// Pass remaining arguments to cargo test after all options and after `--`.
     #[arg(last = true, help_heading = "Execution")]
     cargo_test_args: Vec<String>,

src/options.rs

@@ -290,10 +290,13 @@ impl Options {
 
         let options = Options {
             additional_cargo_args: join_slices(&args.cargo_arg, &config.additional_cargo_args),
-            additional_cargo_test_args: join_slices(
-                &args.cargo_test_args,
-                &config.additional_cargo_test_args,
-            ),
+            additional_cargo_test_args: args
+                .cargo_test_arg
+                .iter()
+                .chain(&args.cargo_test_args)
+                .chain(&config.additional_cargo_test_args)
+                .cloned()
+                .collect(),
             all_features: args.all_features || config.all_features.unwrap_or(false),
             annotations: args.annotations.resolve(),
             baseline: args.baseline,
@@ -1097,4 +1100,77 @@ mod test {
         let options = Options::new(&args, &config).unwrap();
         assert!(!options.copy_vcs);
     }
+
+    #[test]
+    fn cargo_test_arg_from_command_line() {
+        let args = Args::parse_from(["mutants", "--cargo-test-arg=--lib"]);
+        let config = Config::default();
+        let options = Options::new(&args, &config).unwrap();
+        assert_eq!(options.additional_cargo_test_args, vec!["--lib"]);
+    }
+
+    #[test]
+    fn cargo_test_arg_multiple_from_command_line() {
+        let args = Args::parse_from([
+            "mutants",
+            "--cargo-test-arg=--lib",
+            "--cargo-test-arg=--no-fail-fast",
+        ]);
+        let config = Config::default();
+        let options = Options::new(&args, &config).unwrap();
+        assert_eq!(
+            options.additional_cargo_test_args,
+            vec!["--lib", "--no-fail-fast"]
+        );
+    }
+
+    #[test]
+    fn cargo_test_args_after_double_dash() {
+        let args = Args::parse_from(["mutants", "--", "--lib", "--no-fail-fast"]);
+        let config = Config::default();
+        let options = Options::new(&args, &config).unwrap();
+        assert_eq!(
+            options.additional_cargo_test_args,
+            vec!["--lib", "--no-fail-fast"]
+        );
+    }
+
+    #[test]
+    fn cargo_test_arg_and_cargo_test_args_combined() {
+        let args = Args::parse_from(["mutants", "--cargo-test-arg=--lib", "--", "--no-fail-fast"]);
+        let config = Config::default();
+        let options = Options::new(&args, &config).unwrap();
+        assert_eq!(
+            options.additional_cargo_test_args,
+            vec!["--lib", "--no-fail-fast"]
+        );
+    }
+
+    #[test]
+    fn cargo_test_arg_and_config_combined() {
+        let args = Args::parse_from(["mutants", "--cargo-test-arg=--lib"]);
+        let config = Config::from_str(indoc! { r#"
+            additional_cargo_test_args = ["--no-fail-fast"]
+        "#})
+        .unwrap();
+        let options = Options::new(&args, &config).unwrap();
+        assert_eq!(
+            options.additional_cargo_test_args,
+            vec!["--lib", "--no-fail-fast"]
+        );
+    }
+
+    #[test]
+    fn cargo_test_arg_cargo_test_args_and_config_combined() {
+        let args = Args::parse_from(["mutants", "--cargo-test-arg=--all-targets", "--", "--lib"]);
+        let config = Config::from_str(indoc! { r#"
+            additional_cargo_test_args = ["--no-fail-fast"]
+        "#})
+        .unwrap();
+        let options = Options::new(&args, &config).unwrap();
+        assert_eq!(
+            options.additional_cargo_test_args,
+            vec!["--all-targets", "--lib", "--no-fail-fast"]
+        );
+    }
 }

tests/config.rs

@@ -269,6 +269,47 @@ fn additional_cargo_test_args() {
         .success();
 }
 
+#[test]
+fn cargo_test_arg_option() {
+    let testdata = copy_of_testdata("fails_without_feature");
+    run()
+        .args(["mutants", "--cargo-test-arg=--all-features", "-d"])
+        .arg(testdata.path())
+        .assert()
+        .success();
+}
+
+#[test]
+fn cargo_test_arg_multiple_options() {
+    let testdata = copy_of_testdata("fails_without_feature");
+    run()
+        .args([
+            "mutants",
+            "--cargo-test-arg=--all-features",
+            "--cargo-test-arg=--no-fail-fast",
+            "-d",
+        ])
+        .arg(testdata.path())
+        .assert()
+        .success();
+}
+
+#[test]
+fn cargo_test_arg_and_additional_cargo_test_args_combined() {
+    let testdata = copy_of_testdata("fails_without_feature");
+    write_config_file(
+        &testdata,
+        r#"
+        additional_cargo_test_args = ["--no-fail-fast"]
+        "#,
+    );
+    run()
+        .args(["mutants", "--cargo-test-arg=--all-features", "-d"])
+        .arg(testdata.path())
+        .assert()
+        .success();
+}
+
 #[test]
 fn features_config_option() {
     let testdata = copy_of_testdata("fails_without_feature");