codex/prs/bolinfest/study/PR-1542-study.md

DOs

• Use Raw Strings for SSE/JSON: Prefer r#"... "# when not formatting to avoid escaping braces and quotes.

let sse = r#"data: {"choices":[{"delta":{"content":"hi"}}]}

data: {"choices":[{"delta":{}}]}

data: [DONE]
"#;

• Run Binaries With cargo_bin: Use assert_cmd to execute the compiled CLI instead of spawning cargo run.

use assert_cmd::prelude::*;
use std::process::Command;

let mut cmd = Command::cargo_bin("codex-cli").unwrap();
cmd.arg("exec")
   .arg("--skip-git-repo-check")
   .arg("-c")
   .arg(format!(
       "model_providers.mock={{ name=\"mock\", base_url=\"{}/v1\", env_key=\"PATH\", wire_api=\"chat\" }}",
       server.uri()
   ))
   .arg("-c")
   .arg("model_provider=mock")
   .arg("-C")
   .arg(env!("CARGO_MANIFEST_DIR"))
   .arg("hello?")
   .env("CODEX_HOME", home.path())
   .env("OPENAI_API_KEY", "dummy")
   .env("OPENAI_BASE_URL", format!("{}/v1", server.uri()))
   .assert()
   .success();

• Set Working Dir Via -C/--cd: Ask the CLI to change directories rather than mutating the test process’s CWD.

let mut cmd = Command::cargo_bin("codex-cli").unwrap();
cmd.args(["exec", "-C", env!("CARGO_MANIFEST_DIR"), "hello?"]);

• Terminate Streams With [DONE]: Include the [DONE] sentinel in mock SSE streams; use empty {} deltas only as interim chunks.

let sse = r#"data: {"choices":[{"delta":{"content":"hi"}}]}

data: {"choices":[{"delta":{}}]}

data: [DONE]
"#;

DON’Ts

• Don’t Over‑Escape JSON/SSE: Avoid concat! with escaped quotes/braces when a raw string will do.

// Bad
let sse = concat!(
  "data: {\"choices\":[{\"delta\":{\"content\":\"hi\"}}]}\n\n",
  "data: {\"choices\":[{\"delta\":{}}]}\n\n",
  "data: [DONE]\n\n",
);

• Don’t Spawn cargo run Unless Necessary: It’s slower and less direct than running the binary under test.

// Bad
let mut cmd = std::process::Command::new("cargo");
cmd.args(["run", "-p", "codex-cli", "--", "exec", "hello?"]);

• Don’t Rely on current_dir When CLI Supports -C: Prefer the CLI’s own directory flag for reproducibility and clarity.

// Bad
cmd.current_dir(env!("CARGO_MANIFEST_DIR"));

• Don’t Treat Empty {} as End‑Of‑Stream: Without [DONE], completion is ambiguous.

// Bad: missing [DONE]
let sse = r#"data: {"choices":[{"delta":{"content":"hi"}}]}

data: {"choices":[{"delta":{}}]}
"#;