A contract meets real rows.

TokMesh Lite already knew how to parse a YAML manifest and validate CSV data. This session gave that engine a concrete, runnable learning product. All records are explicitly synthetic: they are test data, not claims about real mines, operators, reserves, grades, or production.

examples/nigeria-lithium/
├── product.yaml   # contract: schema + quality + ownership
├── valid.csv      # eight rows expected to pass
└── invalid.csv    # eight rows with controlled defects

We used two already agreed public seams: the CLI process boundary for exit behavior and validate_data for detailed issue reports. We did not test private helper functions.

Report-level test pattern

#[test]
fn nigeria_lithium_invalid_example_rejects_missing_site_name() {
    let root = std::path::Path::new(env!("CARGO_MANIFEST_DIR"));
    let manifest_path = root.join("examples/nigeria-lithium/product.yaml");
    let data_path = root.join("examples/nigeria-lithium/invalid.csv");

    let manifest = load_manifest(&manifest_path).expect("manifest should parse");
    let report = validate_data(&manifest, &data_path)
        .expect("CSV should be readable");

    assert!(report.issues.iter().any(|issue| {
        issue.code == "data.value.required"
            && issue.location == "row[6].site_name"
    }));
}

CLI process test pattern

let status = Command::new(env!("CARGO_BIN_EXE_tokmesh-lite"))
    .args([
        "data",
        "validate",
        &format!("{root}/examples/nigeria-lithium/product.yaml"),
        &format!("{root}/examples/nigeria-lithium/invalid.csv"),
    ])
    .status()
    .expect("CLI should run");

assert_eq!(status.code(), Some(1));

Why the focused test command has two separators

cargo test --test validation TEST_NAME -- --exact
│     │    │                 │         └─ argument for Rust test harness
│     │    │                 └────────── separator: Cargo stops parsing here
│     │    └──────────────────────────── integration-test target
│     └───────────────────────────────── run tests
└─────────────────────────────────────── Rust package manager/build tool

git status
git add tests/cli.rs tests/validation.rs \
  examples/nigeria-lithium/product.yaml \
  examples/nigeria-lithium/valid.csv \
  examples/nigeria-lithium/invalid.csv
git diff --cached --check
git commit -m "feat: add Nigeria lithium validation example"
git push origin main

GitHub’s repository viewer is a source-code browser. Clicking an HTML file under github.com/.../blob/... shows its source. GitHub Pages is the static web host that renders the same committed HTML.

main branch
└── docs/                      # configured Pages source
    ├── .nojekyll              # publish static files directly
    ├── index.html             # default learning-library home
    └── sessions/
        ├── 2026-08-20-session-01.html
        └── 2026-08-22-session-02.html

Open the rendered TokMesh Lite learning library

cargo fmt --check
# passed with no output

cargo clippy --all-targets --all-features -- -D warnings
Finished dev profile ...

cargo test
tests/cli.rs:        4 passed; 0 failed
tests/validation.rs: 7 passed; 0 failed
doc tests:           0 failed

INVALID — 4 issue(s)
- [quality.unique.duplicate] row[3].site_id
- [quality.accepted_values.rejected] row[4].jurisdiction
- [quality.range.outside] row[5].li2o_grade_percent
- [data.value.required] row[6].site_name

The suite contains 11 executable integration tests in total. The invalid CLI output demonstrates four simultaneous findings while the focused report tests prove three of them by exact code and location. Duplicate-ID behavior is also confirmed by the CLI test and output.