Rust learning: lessons, notes, and exercise crates

tasks/tests/collections.rs

@@ -0,0 +1,166 @@
+// The 0008 specification, as executable tests. Do not edit this file — make it pass.
+// Copy to: tasks/tests/collections.rs
+// Run with: cargo test
+
+use std::collections::HashMap;
+use std::path::PathBuf;
+use std::sync::atomic::{AtomicU32, Ordering};
+use tasks::stats::tally;
+use tasks::store::Store;
+use tasks::task::Priority;
+
+// 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-coll-{}-{}.txt", std::process::id(), n))
+}
+
+// ---------- tally: one generic function, any element type, any key type ----------
+
+#[test]
+fn tally_counts_how_often_each_key_appears() {
+    let words = ["red", "blue", "red", "green", "red"];
+    let counts = tally(&words, |word| *word);
+    assert_eq!(counts[&"red"], 3);
+    assert_eq!(counts[&"blue"], 1);
+    assert_eq!(counts.len(), 3);
+}
+
+#[test]
+fn tally_accepts_a_key_type_that_is_not_the_element_type() {
+    let words = ["a", "bb", "cc", "ddd"];
+    let by_length = tally(&words, |word| word.len());
+    assert_eq!(by_length, HashMap::from([(1, 1), (2, 2), (3, 1)]));
+}
+
+#[test]
+fn tally_of_nothing_is_an_empty_map() {
+    let nothing: [u32; 0] = [];
+    assert!(tally(&nothing, |n| *n).is_empty());
+}
+
+// ---------- counting the store, built on that same function ----------
+
+#[test]
+fn count_by_priority_counts_every_priority_present() {
+    let mut store = Store::new();
+    store.add("buy milk", Priority::High);
+    store.add("call bank", Priority::High);
+    store.add("water plants", Priority::Low);
+
+    assert_eq!(
+        store.count_by_priority(),
+        HashMap::from([(Priority::High, 2), (Priority::Low, 1)])
+    );
+}
+
+#[test]
+fn count_by_priority_has_no_entry_for_an_absent_priority() {
+    let mut store = Store::new();
+    store.add("buy milk", Priority::High);
+
+    let counts = store.count_by_priority();
+    assert_eq!(counts.len(), 1, "absent priorities must not appear as zero");
+    assert_eq!(counts.get(&Priority::Low), None);
+}
+
+#[test]
+fn count_by_priority_of_an_empty_store_is_empty() {
+    assert!(Store::new().count_by_priority().is_empty());
+}
+
+// ---------- selecting titles: filter, map, collect ----------
+
+#[test]
+fn titles_with_returns_matching_titles_in_order() {
+    let mut store = Store::new();
+    store.add("buy milk", Priority::High);
+    store.add("water plants", Priority::Low);
+    store.add("call bank", Priority::High);
+
+    assert_eq!(store.titles_with(Priority::High), ["buy milk", "call bank"]);
+}
+
+#[test]
+fn titles_with_returns_nothing_when_no_task_matches() {
+    let mut store = Store::new();
+    store.add("buy milk", Priority::High);
+
+    assert!(store.titles_with(Priority::Medium).is_empty());
+}
+
+// ---------- clearing out finished work: retain ----------
+
+#[test]
+fn remove_completed_drops_done_tasks_and_reports_how_many() {
+    let mut store = Store::new();
+    let first = store.add("buy milk", Priority::High);
+    store.add("water plants", Priority::Low);
+    let third = store.add("call bank", Priority::Medium);
+    store.complete(first).unwrap();
+    store.complete(third).unwrap();
+
+    assert_eq!(store.remove_completed(), 2);
+    assert_eq!(store.titles_with(Priority::Low), ["water plants"]);
+    assert_eq!(store.tasks().len(), 1);
+}
+
+#[test]
+fn remove_completed_removes_nothing_when_nothing_is_done() {
+    let mut store = Store::new();
+    store.add("buy milk", Priority::High);
+    store.add("call bank", Priority::Low);
+
+    assert_eq!(store.remove_completed(), 0);
+    assert_eq!(store.tasks().len(), 2);
+}
+
+#[test]
+fn remove_completed_keeps_the_remaining_ids_unchanged() {
+    let mut store = Store::new();
+    let first = store.add("buy milk", Priority::High);
+    store.add("call bank", Priority::Low);
+    store.complete(first).unwrap();
+    store.remove_completed();
+
+    assert_eq!(store.tasks()[0].id, 2, "surviving tasks keep their own id");
+    assert_eq!(
+        store.add("new one", Priority::Low),
+        3,
+        "and the counter is untouched"
+    );
+}
+
+// ---------- load: one collect, and the line rules that come with it ----------
+
+#[test]
+fn a_file_without_a_trailing_newline_still_loads() {
+    let path = temp_path();
+    std::fs::write(&path, "1|todo|low|fine").unwrap();
+
+    let store = Store::load(&path).unwrap();
+    assert_eq!(store.tasks().len(), 1);
+}
+
+#[test]
+fn a_blank_line_inside_the_file_is_a_bad_line() {
+    let path = temp_path();
+    std::fs::write(&path, "1|todo|low|fine\n\n2|todo|low|also fine\n").unwrap();
+
+    let err = Store::load(&path).unwrap_err();
+    assert_eq!(err.to_string(), "cannot read saved line: ");
+}
+
+#[test]
+fn one_bad_line_loses_the_whole_load_not_part_of_it() {
+    let path = temp_path();
+    std::fs::write(&path, "1|todo|low|fine\nrubbish\n3|todo|low|also fine\n").unwrap();
+
+    assert!(Store::load(&path).is_err());
+    // the file itself is untouched by a failed load — nothing was half-written
+    assert_eq!(
+        std::fs::read_to_string(&path).unwrap(),
+        "1|todo|low|fine\nrubbish\n3|todo|low|also fine\n"
+    );
+}