feat(test): own process startup and cleanup

hemx-test/tests/process.rs

@@ -0,0 +1,31 @@
+use hemx_test::TestProcess;
+use std::process::Command;
+use std::time::Duration;
+
+#[test]
+fn process_harness_reports_early_exit_with_context() {
+    // req: test/019
+    let mut command = Command::new(std::env::current_exe().expect("current test executable"));
+    command
+        .arg("--exact")
+        .arg("helper_process_exits_successfully")
+        .arg("--nocapture");
+
+    let error = match TestProcess::start(
+        command,
+        "short-lived helper",
+        "127.0.0.1:9",
+        Duration::from_secs(2),
+    ) {
+        Ok(_) => panic!("a process that exits before readiness must fail startup"),
+        Err(error) => error,
+    };
+    let message = error.to_string();
+
+    assert!(message.contains("short-lived helper"), "{message}");
+    assert!(message.contains("127.0.0.1:9"), "{message}");
+    assert!(message.contains("exited with"), "{message}");
+}
+
+#[test]
+fn helper_process_exits_successfully() {}