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

NEWS.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- New: `--cargo-test-arg` option to pass additional arguments to `cargo test`.
+
 - New: `--sharding` option to control how mutants are distributed across multiple machines, with choices of `slice` or `round-robin`.
 
 - Changed: The default sharding strategy is now `slice`; previously it was `round-robin`. Sliced sharding gives each worker better locality of reference due to testing changes to related packages, but may make the runtime more uneven between workers if some packages are slower to test than others.

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=--lib
+```
+
+Both formats can be used together if needed:
+
+```shell
+cargo mutants --cargo-test-arg=--lib -- --all-targets
+```
+
 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

@@ -221,6 +221,10 @@ 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

@@ -324,10 +324,13 @@ 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,
@@ -1146,6 +1149,79 @@ mod test {
         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"]
+        );
+    }
+
     #[test]
     fn sharding() {
         let args = Args::try_parse_from(["mutants", "--sharding=slice", "--shard=0/10"]).unwrap();

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");