feat: Update version to 0.4.0, add test command, and improve documentation for testing functionality

tests/cli_basic.rs

@@ -1,7 +1,7 @@
 use std::path::{Path, PathBuf};
 use std::process::Command;
-use std::sync::Once;
 use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::Once;
 use std::time::{SystemTime, UNIX_EPOCH};
 
 static COUNTER: AtomicUsize = AtomicUsize::new(0);
@@ -218,3 +218,31 @@ fn workspace_build_and_clean_all() {
         "root target/debug should remain"
     );
 }
+
+#[test]
+fn dcr_test_runs_without_sandbox_dependency() {
+    let Some(compiler) = available_compiler() else {
+        eprintln!("no compiler found; skipping dcr test integration");
+        return;
+    };
+
+    let dir = unique_sandbox_dir("dcr_test_independent");
+    let out = run_dcr(&["init"], &dir);
+    assert!(out.status.success(), "dcr init should succeed");
+
+    let envs = [("DCR_CC", compiler)];
+    let out_init = run_dcr_env(&["test", "--init"], &dir, &envs);
+    assert!(out_init.status.success(), "dcr test --init should succeed");
+
+    let out = run_dcr_env(&["test"], &dir, &envs);
+    assert!(out.status.success(), "dcr test should succeed");
+    let stdout = String::from_utf8_lossy(&out.stdout);
+    let stderr = String::from_utf8_lossy(&out.stderr);
+    assert!(stdout.contains("TOTAL: 1"), "TOTAL summary line missing");
+    assert!(
+        stdout.contains("PASS:  1"),
+        "PASS summary line missing\nstdout:\n{}\nstderr:\n{}",
+        stdout,
+        stderr
+    );
+}