Rust learning: lessons, notes, and exercise crates

tasks/tests/persist.rs

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+// The 0007 specification, as executable tests. Do not edit this file — make it pass.
+// Copy to: tasks/tests/persist.rs
+// Run with: cargo test
+
+use std::error::Error;
+use std::path::PathBuf;
+use std::sync::atomic::{AtomicU32, Ordering};
+use tasks::error::TaskError;
+use tasks::store::Store;
+use tasks::task::{Priority, Status, Task};
+
+// a fresh path per test, inside the OS temp dir — no file is ever left in your crate
+fn temp_path() -> PathBuf {
+    static N: AtomicU32 = AtomicU32::new(0);
+    let n = N.fetch_add(1, Ordering::Relaxed);
+    std::env::temp_dir().join(format!("tasks-test-{}-{}.txt", std::process::id(), n))
+}
+
+// ---------- a Task survives the trip to text and back ----------
+
+#[test]
+fn a_task_becomes_a_line_and_a_line_becomes_a_task() {
+    let task = Task {
+        id: 3,
+        title: String::from("buy milk"),
+        priority: Priority::High,
+        status: Status::Done,
+    };
+    assert_eq!(task.to_line(), "3|done|high|buy milk");
+    assert_eq!("3|done|high|buy milk".parse::<Task>().unwrap(), task);
+}
+
+#[test]
+fn a_title_may_contain_the_separator() {
+    let line = "1|todo|low|read a|b testing";
+    let task: Task = line.parse().unwrap();
+    assert_eq!(task.title, "read a|b testing");
+    assert_eq!(task.to_line(), line);
+}
+
+#[test]
+fn a_corrupt_line_names_itself() {
+    for bad in ["", "nonsense", "1|todo|low", "x|todo|low|t", "1|sleeping|low|t", "1|todo|urgent|t"] {
+        assert_eq!(
+            bad.parse::<Task>().unwrap_err(),
+            TaskError::BadLine(bad.to_string()),
+            "line {:?} should be reported as a bad line",
+            bad
+        );
+    }
+}
+
+// ---------- the store round trip ----------
+
+#[test]
+fn every_task_survives_save_then_load() {
+    let path = temp_path();
+    let mut store = Store::new();
+    store.add("buy milk", Priority::High);
+    let second = store.add("call bank", Priority::Medium);
+    store.complete(second).unwrap();
+    store.save(&path).unwrap();
+
+    let loaded = Store::load(&path).unwrap();
+    assert_eq!(loaded.tasks(), store.tasks());
+}
+
+#[test]
+fn ids_do_not_restart_after_a_reload() {
+    let path = temp_path();
+    let mut store = Store::new();
+    store.add("first", Priority::Low);
+    store.add("second", Priority::Low);
+    store.save(&path).unwrap();
+
+    let mut loaded = Store::load(&path).unwrap();
+    assert_eq!(loaded.add("third", Priority::Low), 3);
+}
+
+#[test]
+fn a_missing_file_is_an_empty_store_not_an_error() {
+    let path = temp_path(); // never created
+    let store = Store::load(&path).expect("first run must not fail");
+    assert!(store.tasks().is_empty());
+}
+
+#[test]
+fn a_corrupt_file_fails_loudly() {
+    let path = temp_path();
+    std::fs::write(&path, "1|todo|low|fine\nrubbish\n").unwrap();
+    assert_eq!(
+        Store::load(&path).unwrap_err(),
+        TaskError::BadLine(String::from("rubbish"))
+    );
+}
+
+// ---------- io::Error becomes TaskError, and keeps its cause ----------
+
+#[test]
+fn a_write_that_cannot_happen_is_an_io_error() {
+    let path = temp_path().join("no-such-dir").join("t.txt");
+    let err = Store::new().save(&path).unwrap_err();
+    assert!(matches!(err, TaskError::Io(_)), "got {:?}", err);
+    assert_eq!(err.to_string(), "cannot read or write the task file");
+    assert!(err.source().is_some(), "the io::Error must stay reachable");
+}