Wave 5: Schemas command, sync command, network policy, test fixtures (bd-x15, bd-3f4, bd-1cv, bd-lx6)

- Implement schemas command with list/show modes, regex filtering, ref expansion
- Implement sync command with conditional fetch, content hash diffing, dry-run
- Add NetworkPolicy enum (Auto/Offline/OnlineOnly) with env var + CLI flag resolution
- Integrate network policy into AsyncHttpClient and fetch command
- Create test fixtures (petstore.json/yaml, minimal.json) and integration test helpers
- Fix clippy lints: derivable_impls, len_zero, borrow-after-move, deprecated API
- 192 tests passing (179 unit + 13 integration), all quality gates green

tests/helpers/mod.rs

@@ -0,0 +1,134 @@
+use std::path::{Path, PathBuf};
+
+use assert_cmd::Command;
+use tempfile::TempDir;
+
+/// An isolated test environment with its own home, cache, and config directories.
+///
+/// Setting `SWAGGER_CLI_HOME` on each command invocation ensures tests never
+/// touch the real user cache or config.
+pub struct TestEnv {
+    // Kept alive for RAII cleanup; not read directly.
+    _temp_dir: TempDir,
+    pub home_dir: PathBuf,
+    pub cache_dir: PathBuf,
+    pub config_dir: PathBuf,
+}
+
+impl TestEnv {
+    /// Creates a fresh isolated test environment backed by a temporary directory.
+    pub fn new() -> Self {
+        let temp_dir = TempDir::new().expect("failed to create temp dir");
+        let home_dir = temp_dir.path().join("swagger-cli-home");
+        let cache_dir = home_dir.join("cache");
+        let config_dir = home_dir.join("config");
+
+        std::fs::create_dir_all(&cache_dir).expect("failed to create cache dir");
+        std::fs::create_dir_all(&config_dir).expect("failed to create config dir");
+
+        Self {
+            _temp_dir: temp_dir,
+            home_dir,
+            cache_dir,
+            config_dir,
+        }
+    }
+}
+
+/// Run `swagger-cli` with the given arguments inside the provided test environment.
+///
+/// `SWAGGER_CLI_HOME` is set so all reads/writes go to the temp directory.
+#[allow(deprecated)]
+pub fn run_cmd(env: &TestEnv, args: &[&str]) -> assert_cmd::assert::Assert {
+    Command::cargo_bin("swagger-cli")
+        .expect("binary not found -- run `cargo build` first")
+        .env("SWAGGER_CLI_HOME", &env.home_dir)
+        .args(args)
+        .assert()
+}
+
+/// Fetch a fixture file into the test environment's cache under the given alias.
+///
+/// Runs: `swagger-cli fetch <fixture_path> --alias <alias>`
+pub fn fetch_fixture(env: &TestEnv, fixture_name: &str, alias: &str) {
+    let path = fixture_path(fixture_name);
+    assert!(
+        path.exists(),
+        "fixture file does not exist: {}",
+        path.display()
+    );
+
+    let path_str = path.to_str().expect("fixture path is not valid UTF-8");
+
+    run_cmd(env, &["fetch", path_str, "--alias", alias]).success();
+}
+
+/// Parse robot-mode JSON output from command stdout bytes.
+///
+/// The robot envelope has the shape: `{"ok": true, "data": {...}, "meta": {...}}`
+pub fn parse_robot_json(output: &[u8]) -> serde_json::Value {
+    let text = std::str::from_utf8(output).expect("stdout is not valid UTF-8");
+    serde_json::from_str(text.trim()).expect("stdout is not valid JSON")
+}
+
+/// Return the absolute path to a test fixture file by name.
+///
+/// Fixtures live in `tests/fixtures/` relative to the project root.
+pub fn fixture_path(name: &str) -> PathBuf {
+    let manifest_dir =
+        std::env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set -- run via cargo");
+    Path::new(&manifest_dir)
+        .join("tests")
+        .join("fixtures")
+        .join(name)
+}
+
+// ---------------------------------------------------------------------------
+// Self-tests for the helpers
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_env_creates_directories() {
+        let env = TestEnv::new();
+        assert!(env.home_dir.exists());
+        assert!(env.cache_dir.exists());
+        assert!(env.config_dir.exists());
+    }
+
+    #[test]
+    fn test_fixture_path_exists() {
+        let path = fixture_path("petstore.json");
+        assert!(path.exists(), "petstore.json fixture missing");
+        assert!(path.is_absolute());
+    }
+
+    #[test]
+    fn test_fixture_path_yaml() {
+        let path = fixture_path("petstore.yaml");
+        assert!(path.exists(), "petstore.yaml fixture missing");
+    }
+
+    #[test]
+    fn test_fixture_path_minimal() {
+        let path = fixture_path("minimal.json");
+        assert!(path.exists(), "minimal.json fixture missing");
+    }
+
+    #[test]
+    fn test_parse_robot_json_valid() {
+        let input = br#"{"ok":true,"data":{"x":1},"meta":{}}"#;
+        let val = parse_robot_json(input);
+        assert_eq!(val["ok"], true);
+        assert_eq!(val["data"]["x"], 1);
+    }
+
+    #[test]
+    #[should_panic(expected = "not valid JSON")]
+    fn test_parse_robot_json_invalid() {
+        parse_robot_json(b"not json");
+    }
+}