feat: extract database operations module and add extensive test suite

tests/db_batch_upsert.rs

@@ -0,0 +1,212 @@
+mod helpers;
+
+use banner::data::batch::batch_upsert_courses;
+use sqlx::PgPool;
+
+#[sqlx::test]
+async fn test_batch_upsert_empty_slice(pool: PgPool) {
+    batch_upsert_courses(&[], &pool).await.unwrap();
+
+    let count: (i64,) = sqlx::query_as("SELECT COUNT(*) FROM courses")
+        .fetch_one(&pool)
+        .await
+        .unwrap();
+
+    assert_eq!(count.0, 0);
+}
+
+#[sqlx::test]
+async fn test_batch_upsert_inserts_new_courses(pool: PgPool) {
+    let courses = vec![
+        helpers::make_course("10001", "202510", "CS", "1083", "Intro to CS", 25, 30, 0, 5),
+        helpers::make_course(
+            "10002",
+            "202510",
+            "MAT",
+            "1214",
+            "Calculus I",
+            40,
+            45,
+            3,
+            10,
+        ),
+    ];
+
+    batch_upsert_courses(&courses, &pool).await.unwrap();
+
+    let rows: Vec<(String, String, String, String, i32, i32, i32, i32)> = sqlx::query_as(
+        "SELECT crn, subject, course_number, title, enrollment, max_enrollment, wait_count, wait_capacity
+         FROM courses ORDER BY crn",
+    )
+    .fetch_all(&pool)
+    .await
+    .unwrap();
+
+    assert_eq!(rows.len(), 2);
+
+    let (crn, subject, course_number, title, enrollment, max_enrollment, wait_count, wait_capacity) =
+        &rows[0];
+    assert_eq!(crn, "10001");
+    assert_eq!(subject, "CS");
+    assert_eq!(course_number, "1083");
+    assert_eq!(title, "Intro to CS");
+    assert_eq!(*enrollment, 25);
+    assert_eq!(*max_enrollment, 30);
+    assert_eq!(*wait_count, 0);
+    assert_eq!(*wait_capacity, 5);
+
+    let (crn, subject, ..) = &rows[1];
+    assert_eq!(crn, "10002");
+    assert_eq!(subject, "MAT");
+}
+
+#[sqlx::test]
+async fn test_batch_upsert_updates_existing(pool: PgPool) {
+    let initial = vec![helpers::make_course(
+        "20001",
+        "202510",
+        "CS",
+        "3443",
+        "App Programming",
+        10,
+        35,
+        0,
+        5,
+    )];
+    batch_upsert_courses(&initial, &pool).await.unwrap();
+
+    // Upsert the same CRN+term with updated enrollment
+    let updated = vec![helpers::make_course(
+        "20001",
+        "202510",
+        "CS",
+        "3443",
+        "App Programming",
+        30,
+        35,
+        2,
+        5,
+    )];
+    batch_upsert_courses(&updated, &pool).await.unwrap();
+
+    let count: (i64,) = sqlx::query_as("SELECT COUNT(*) FROM courses")
+        .fetch_one(&pool)
+        .await
+        .unwrap();
+    assert_eq!(count.0, 1, "upsert should not create a duplicate row");
+
+    let (enrollment, wait_count): (i32, i32) =
+        sqlx::query_as("SELECT enrollment, wait_count FROM courses WHERE crn = '20001'")
+            .fetch_one(&pool)
+            .await
+            .unwrap();
+    assert_eq!(enrollment, 30);
+    assert_eq!(wait_count, 2);
+}
+
+#[sqlx::test]
+async fn test_batch_upsert_mixed_insert_and_update(pool: PgPool) {
+    let initial = vec![
+        helpers::make_course("30001", "202510", "CS", "1083", "Intro to CS", 10, 30, 0, 5),
+        helpers::make_course(
+            "30002",
+            "202510",
+            "CS",
+            "2073",
+            "Computer Architecture",
+            20,
+            30,
+            0,
+            5,
+        ),
+    ];
+    batch_upsert_courses(&initial, &pool).await.unwrap();
+
+    // Update both existing courses and add a new one
+    let mixed = vec![
+        helpers::make_course("30001", "202510", "CS", "1083", "Intro to CS", 15, 30, 1, 5),
+        helpers::make_course(
+            "30002",
+            "202510",
+            "CS",
+            "2073",
+            "Computer Architecture",
+            25,
+            30,
+            0,
+            5,
+        ),
+        helpers::make_course(
+            "30003",
+            "202510",
+            "MAT",
+            "1214",
+            "Calculus I",
+            40,
+            45,
+            3,
+            10,
+        ),
+    ];
+    batch_upsert_courses(&mixed, &pool).await.unwrap();
+
+    let count: (i64,) = sqlx::query_as("SELECT COUNT(*) FROM courses")
+        .fetch_one(&pool)
+        .await
+        .unwrap();
+    assert_eq!(count.0, 3, "should have 2 updated + 1 new = 3 total rows");
+
+    // Verify updated values
+    let (enrollment,): (i32,) =
+        sqlx::query_as("SELECT enrollment FROM courses WHERE crn = '30001'")
+            .fetch_one(&pool)
+            .await
+            .unwrap();
+    assert_eq!(enrollment, 15);
+
+    let (enrollment,): (i32,) =
+        sqlx::query_as("SELECT enrollment FROM courses WHERE crn = '30002'")
+            .fetch_one(&pool)
+            .await
+            .unwrap();
+    assert_eq!(enrollment, 25);
+
+    // Verify new row
+    let (subject,): (String,) = sqlx::query_as("SELECT subject FROM courses WHERE crn = '30003'")
+        .fetch_one(&pool)
+        .await
+        .unwrap();
+    assert_eq!(subject, "MAT");
+}
+
+#[sqlx::test]
+async fn test_batch_upsert_unique_constraint_crn_term(pool: PgPool) {
+    // Same CRN, different term codes → should produce two separate rows
+    let courses = vec![
+        helpers::make_course("40001", "202510", "CS", "1083", "Intro to CS", 25, 30, 0, 5),
+        helpers::make_course("40001", "202520", "CS", "1083", "Intro to CS", 10, 30, 0, 5),
+    ];
+
+    batch_upsert_courses(&courses, &pool).await.unwrap();
+
+    let count: (i64,) = sqlx::query_as("SELECT COUNT(*) FROM courses WHERE crn = '40001'")
+        .fetch_one(&pool)
+        .await
+        .unwrap();
+    assert_eq!(
+        count.0, 2,
+        "same CRN with different term codes should be separate rows"
+    );
+
+    let rows: Vec<(String, i32)> = sqlx::query_as(
+        "SELECT term_code, enrollment FROM courses WHERE crn = '40001' ORDER BY term_code",
+    )
+    .fetch_all(&pool)
+    .await
+    .unwrap();
+
+    assert_eq!(rows[0].0, "202510");
+    assert_eq!(rows[0].1, 25);
+    assert_eq!(rows[1].0, "202520");
+    assert_eq!(rows[1].1, 10);
+}