date-time: add test

date_time/tests/v0.rs

@@ -0,0 +1,32 @@
+use std::{convert::TryFrom, str::FromStr};
+
+use date_time::{Instant, OffsetDateTime};
+
+#[test]
+fn use_case_plus_days() -> anyhow::Result<()> {
+    let plus_days =
+        |offset_date_time: OffsetDateTime, days: u64| -> anyhow::Result<OffsetDateTime> {
+            // TODO: offset_date_time + duration
+            let instant = offset_date_time.instant();
+            let time_zone_offset = offset_date_time.time_zone_offset();
+
+            // TODO: instant + duration
+            let seconds = u64::from(instant);
+            let updated_seconds = seconds + days * 86400;
+            let updated_instant = Instant::try_from(updated_seconds)?;
+
+            let updated_offset_date_time =
+                OffsetDateTime::from_instant(updated_instant, time_zone_offset);
+            Ok(updated_offset_date_time)
+        };
+
+    let offset_date_time = OffsetDateTime::from_str("2021-02-03T04:05:06+09:00")?;
+    let days = 2;
+    let updated_offset_date_time = plus_days(offset_date_time, days)?;
+    assert_eq!(
+        updated_offset_date_time.to_string(),
+        "2021-02-05T04:05:06+09:00"
+    );
+
+    Ok(())
+}