date: add tests

src/items/builder.rs

@@ -333,3 +333,146 @@ impl TryFrom<Vec<Item>> for DateTimeBuilder {
         Ok(builder)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Helper functions to create test items by parsing
+    fn timestamp() -> epoch::Timestamp {
+        let mut input = "@1234567890";
+        epoch::parse(&mut input).unwrap()
+    }
+
+    fn date() -> date::Date {
+        let mut input = "2023-06-15";
+        date::parse(&mut input).unwrap()
+    }
+
+    fn time() -> time::Time {
+        let mut input = "12:30:00";
+        time::parse(&mut input).unwrap()
+    }
+
+    fn time_with_offset() -> time::Time {
+        let mut input = "12:30:00+05:00";
+        time::parse(&mut input).unwrap()
+    }
+
+    fn weekday() -> weekday::Weekday {
+        let mut input = "monday";
+        weekday::parse(&mut input).unwrap()
+    }
+
+    fn offset() -> offset::Offset {
+        let mut input = "+05:00";
+        offset::timezone_offset(&mut input).unwrap()
+    }
+
+    fn relative() -> relative::Relative {
+        let mut input = "1 day";
+        relative::parse(&mut input).unwrap()
+    }
+
+    fn timezone() -> jiff::tz::TimeZone {
+        jiff::tz::TimeZone::UTC
+    }
+
+    #[test]
+    fn test_duplicate_items_errors() {
+        let test_cases = vec![
+            (
+                vec![Item::TimeZone(timezone()), Item::TimeZone(timezone())],
+                "timezone rule cannot appear more than once",
+            ),
+            (
+                vec![Item::Timestamp(timestamp()), Item::Timestamp(timestamp())],
+                "timestamp cannot appear more than once",
+            ),
+            (
+                vec![Item::Date(date()), Item::Date(date())],
+                "date cannot appear more than once",
+            ),
+            (
+                vec![Item::Time(time()), Item::Time(time())],
+                "time cannot appear more than once",
+            ),
+            (
+                vec![Item::Weekday(weekday()), Item::Weekday(weekday())],
+                "weekday cannot appear more than once",
+            ),
+            (
+                vec![Item::Offset(offset()), Item::Offset(offset())],
+                "time offset cannot appear more than once",
+            ),
+        ];
+
+        for (items, expected_err) in test_cases {
+            let result = DateTimeBuilder::try_from(items);
+            assert_eq!(result.unwrap_err(), expected_err);
+        }
+    }
+
+    #[test]
+    fn test_timestamp_cannot_be_combined_with_other_items() {
+        let test_cases = vec![
+            vec![Item::Date(date()), Item::Timestamp(timestamp())],
+            vec![Item::Time(time()), Item::Timestamp(timestamp())],
+            vec![Item::Weekday(weekday()), Item::Timestamp(timestamp())],
+            vec![Item::Offset(offset()), Item::Timestamp(timestamp())],
+            vec![Item::Relative(relative()), Item::Timestamp(timestamp())],
+            vec![Item::Timestamp(timestamp()), Item::Date(date())],
+            vec![Item::Timestamp(timestamp()), Item::Time(time())],
+            vec![Item::Timestamp(timestamp()), Item::Weekday(weekday())],
+            vec![Item::Timestamp(timestamp()), Item::Relative(relative())],
+            vec![Item::Timestamp(timestamp()), Item::Offset(offset())],
+            vec![Item::Timestamp(timestamp()), Item::Pure("2023".to_string())],
+        ];
+
+        for items in test_cases {
+            let result = DateTimeBuilder::try_from(items);
+            assert_eq!(
+                result.unwrap_err(),
+                "timestamp cannot be combined with other date/time items"
+            );
+        }
+    }
+
+    #[test]
+    fn test_time_offset_conflicts() {
+        // Time with offset followed by separate Offset item
+        let items1 = vec![Item::Time(time_with_offset()), Item::Offset(offset())];
+        assert_eq!(
+            DateTimeBuilder::try_from(items1).unwrap_err(),
+            "time offset cannot appear more than once"
+        );
+
+        // Offset item followed by Time with offset
+        let items2 = vec![Item::Offset(offset()), Item::Time(time_with_offset())];
+        assert_eq!(
+            DateTimeBuilder::try_from(items2).unwrap_err(),
+            "time offset and timezone are mutually exclusive"
+        );
+    }
+
+    #[test]
+    fn test_valid_combination_date_time() {
+        let items = vec![Item::Date(date()), Item::Time(time())];
+        let result = DateTimeBuilder::try_from(items);
+        assert!(result.is_ok());
+    }
+
+    #[test]
+    fn test_valid_combination_date_weekday() {
+        let items = vec![Item::Date(date()), Item::Weekday(weekday())];
+        let result = DateTimeBuilder::try_from(items);
+        assert!(result.is_ok());
+    }
+
+    #[test]
+    fn test_valid_timestamp_alone() {
+        let items = vec![Item::Timestamp(timestamp())];
+        let result = DateTimeBuilder::try_from(items);
+        assert!(result.is_ok());
+    }
+}

src/items/primitive.rs

@@ -142,3 +142,64 @@ pub(super) fn ctx_err(reason: &'static str) -> ContextError {
     err.push(StrContext::Expected(StrContextValue::Description(reason)));
     err
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_dec_int() {
+        for (input, expected) in [
+            ("123", 123),                 // positive without sign
+            ("+123", 123),                // positive with '+' sign
+            ("-123", -123),               // negative with '-' sign
+            ("0", 0),                     // zero
+            ("+0", 0),                    // zero with '+' sign
+            ("-0", 0),                    // zero with '-' sign (parses as 0)
+            ("012", 12),                  // zero-prefixed (the main reason for this function)
+            ("+012", 12),                 // zero-prefixed with '+' sign
+            ("-012", -12),                // zero-prefixed with '-' sign
+            ("00123", 123),               // multiple leading zeros
+            ("2147483647", 2147483647),   // i32::MAX
+            ("-2147483648", -2147483648), // i32::MIN
+        ] {
+            let mut s = input;
+            assert_eq!(
+                dec_int::<ContextError>(&mut s).unwrap(),
+                expected,
+                "{input}"
+            );
+        }
+
+        for input in [
+            "",    // empty string
+            "+",   // sign without digits
+            "-",   // sign without digits
+            "abc", // non-numeric
+            "12a", // starts with digits but has non-digit after (but should parse "12" successfully)
+        ] {
+            let mut s = input;
+            let result = dec_int::<ContextError>(&mut s);
+            // Note: "12a" will actually succeed and parse "12", leaving "a" unparsed
+            if input == "12a" {
+                assert_eq!(result.unwrap(), 12, "{input}");
+                assert_eq!(s, "a", "Should leave 'a' unparsed");
+            } else {
+                assert!(result.is_err(), "{input} should fail");
+            }
+        }
+
+        // Test overflow cases
+        for input in [
+            "2147483648",  // i32::MAX + 1
+            "-2147483649", // i32::MIN - 1
+            "99999999999", // way too large
+        ] {
+            let mut s = input;
+            assert!(
+                dec_int::<ContextError>(&mut s).is_err(),
+                "{input} should overflow"
+            );
+        }
+    }
+}

tests/date.rs

@@ -112,3 +112,176 @@ fn test_tz_prefix_with_base_date(#[case] input: &str, #[case] expected: &str) {
         .unwrap();
     check_relative(base, input, expected);
 }
+
+// Test leap year overflow: Feb 29 + years → non-leap year should overflow to March 1
+// This matches GNU date behavior
+#[rstest]
+#[case::feb29_1996_plus_1year("1996-02-29 00:00:00", "1 year", "1997-03-01 00:00:00+00:00")]
+#[case::feb29_2020_plus_1year("2020-02-29 00:00:00", "1 year", "2021-03-01 00:00:00+00:00")]
+#[case::feb29_2000_plus_1year("2000-02-29 00:00:00", "1 year", "2001-03-01 00:00:00+00:00")]
+// Edge case: 0 years should return the same date
+#[case::zero_years("2024-01-15 12:30:45", "0 years", "2024-01-15 12:30:45+00:00")]
+#[case::zero_years_feb29("2020-02-29 00:00:00", "0 years", "2020-02-29 00:00:00+00:00")]
+fn test_leap_year_overflow(#[case] base: &str, #[case] input: &str, #[case] expected: &str) {
+    let now = base
+        .parse::<DateTime>()
+        .unwrap()
+        .to_zoned(TimeZone::UTC)
+        .unwrap();
+    check_relative(now, input, expected);
+}
+
+// Test month arithmetic with day overflow
+// Matches GNU date behavior: when adding months causes day clamping,
+// overflow to next month (e.g., Jan 31 + 1 month = March 2/3, not Feb 28/29)
+#[rstest]
+#[case::jan31_plus_1month_leap("2024-01-31 00:00:00", "1 month", "2024-03-02 00:00:00+00:00")]
+#[case::jan31_plus_1month_nonleap("2023-01-31 00:00:00", "1 month", "2023-03-03 00:00:00+00:00")]
+#[case::mar31_plus_1month("2024-03-31 00:00:00", "1 month", "2024-05-01 00:00:00+00:00")]
+#[case::may31_plus_1month("2024-05-31 00:00:00", "1 month", "2024-07-01 00:00:00+00:00")]
+#[case::rel_2b("1997-01-19 08:17:48", "7 months ago", "1996-06-19 08:17:48+00:00")]
+// Edge case: 0 months should return the same date
+#[case::zero_months("2024-01-31 12:30:45", "0 months", "2024-01-31 12:30:45+00:00")]
+#[case::zero_months_feb29("2020-02-29 00:00:00", "0 months", "2020-02-29 00:00:00+00:00")]
+fn test_month_overflow(#[case] base: &str, #[case] input: &str, #[case] expected: &str) {
+    let now = base
+        .parse::<DateTime>()
+        .unwrap()
+        .to_zoned(TimeZone::UTC)
+        .unwrap();
+    check_relative(now, input, expected);
+}
+
+// Test negative year operations with leap year edge cases
+#[rstest]
+#[case::feb29_minus_1year("2020-02-29 00:00:00", "1 year ago", "2019-03-01 00:00:00+00:00")]
+#[case::feb29_minus_4years("2020-02-29 00:00:00", "4 years ago", "2016-02-29 00:00:00+00:00")]
+#[case::march1_minus_1year("2021-03-01 00:00:00", "1 year ago", "2020-03-01 00:00:00+00:00")]
+fn test_negative_year_operations(#[case] base: &str, #[case] input: &str, #[case] expected: &str) {
+    let now = base
+        .parse::<DateTime>()
+        .unwrap()
+        .to_zoned(TimeZone::UTC)
+        .unwrap();
+    check_relative(now, input, expected);
+}
+
+// Test negative month operations with day overflow
+#[rstest]
+#[case::march31_minus_1month("2024-03-31 00:00:00", "1 month ago", "2024-03-02 00:00:00+00:00")]
+#[case::march31_minus_1month_nonleap(
+    "2023-03-31 00:00:00",
+    "1 month ago",
+    "2023-03-03 00:00:00+00:00"
+)]
+#[case::may31_minus_1month("2024-05-31 00:00:00", "1 month ago", "2024-05-01 00:00:00+00:00")]
+#[case::jan31_minus_1month("2024-01-31 00:00:00", "1 month ago", "2023-12-31 00:00:00+00:00")]
+fn test_negative_month_operations(#[case] base: &str, #[case] input: &str, #[case] expected: &str) {
+    let now = base
+        .parse::<DateTime>()
+        .unwrap()
+        .to_zoned(TimeZone::UTC)
+        .unwrap();
+    check_relative(now, input, expected);
+}
+
+// Test chained operations (multiple relative adjustments in one parse)
+// These ensure that year and month overflow logic works correctly when combined
+#[rstest]
+// Feb 29, 2020 + 1 year = March 1, 2021; + 1 month = April 1, 2021
+#[case::feb29_plus_year_plus_month(
+    "2020-02-29 00:00:00",
+    "1 year 1 month",
+    "2021-04-01 00:00:00+00:00"
+)]
+// Jan 31, 2024 + 1 month = March 2, 2024; + 1 year = March 2, 2025
+#[case::jan31_plus_month_plus_year(
+    "2024-01-31 00:00:00",
+    "1 month 1 year",
+    "2025-03-02 00:00:00+00:00"
+)]
+// Jan 31 + 2 months + 1 day
+#[case::jan31_plus_2months_1day(
+    "2024-01-31 00:00:00",
+    "2 months 1 day",
+    "2024-04-01 00:00:00+00:00"
+)]
+// Feb 29 - 1 year + 1 month (March 1, 2019 + 1 month = April 1, 2019)
+#[case::feb29_minus_year_plus_month(
+    "2020-02-29 00:00:00",
+    "1 year ago 1 month",
+    "2019-04-01 00:00:00+00:00"
+)]
+// Multiple operations with days
+#[case::complex_chain(
+    "2024-01-31 12:30:45",
+    "1 year 2 months 3 days 4 hours",
+    "2025-04-03 16:30:45+00:00"
+)]
+fn test_chained_operations(#[case] base: &str, #[case] input: &str, #[case] expected: &str) {
+    let now = base
+        .parse::<DateTime>()
+        .unwrap()
+        .to_zoned(TimeZone::UTC)
+        .unwrap();
+    check_relative(now, input, expected);
+}
+
+// Test multiple month additions
+// Verifies correct handling when adding multiple months at once
+#[rstest]
+// Jan 31 + 2 months: Jan 31 -> March 31 (no clamping, month has 31 days)
+#[case::jan31_plus_2months("2024-01-31 00:00:00", "2 months", "2024-03-31 00:00:00+00:00")]
+// Jan 31 + 3 months: Jan 31 -> April 30 (clamps), overflow to May 1
+#[case::jan31_plus_3months("2024-01-31 00:00:00", "3 months", "2024-05-01 00:00:00+00:00")]
+// Jan 31 + 6 months: Jan 31 -> July 31 (no overflow)
+#[case::jan31_plus_6months("2024-01-31 00:00:00", "6 months", "2024-07-31 00:00:00+00:00")]
+// Jan 31 + 7 months: Jan 31 -> Aug 31 (no overflow)
+#[case::jan31_plus_7months("2024-01-31 00:00:00", "7 months", "2024-08-31 00:00:00+00:00")]
+// Aug 31 + 6 months: Aug 31 -> Feb 28 (2025 non-leap), overflow to March 3
+#[case::aug31_plus_6months("2024-08-31 00:00:00", "6 months", "2025-03-03 00:00:00+00:00")]
+// May 31 - 3 months: May 31 -> Feb 29 (2024 leap), overflow to March 2
+#[case::may31_minus_3months_leap(
+    "2024-05-31 00:00:00",
+    "3 months ago",
+    "2024-03-02 00:00:00+00:00"
+)]
+// Oct 31 - 8 months: Oct 31 -> Feb 29 (2024 leap), overflow to March 2
+#[case::oct31_minus_8months_leap(
+    "2024-10-31 00:00:00",
+    "8 months ago",
+    "2024-03-02 00:00:00+00:00"
+)]
+fn test_multiple_month_skip(#[case] base: &str, #[case] input: &str, #[case] expected: &str) {
+    let now = base
+        .parse::<DateTime>()
+        .unwrap()
+        .to_zoned(TimeZone::UTC)
+        .unwrap();
+    check_relative(now, input, expected);
+}
+
+// Test embedded timezone handling (cross-TZ-mishandled)
+// When TZ="..." is specified in input with a base date, apply the timezone to the base
+// https://bugs.debian.org/851934#10
+//
+// NOTE: These tests were added without implementation changes.
+// The timezone handling was already working correctly from previous commits.
+// These tests document and verify the expected behavior for this edge case.
+#[rstest]
+#[case::utc_explicit(r#"TZ="UTC0" 1970-01-01 00:00"#, "1970-01-01 00:00:00+00:00")]
+#[case::with_time(r#"TZ="EST5" 1970-01-01 12:30:45"#, "1970-01-01 12:30:45-05:00")]
+#[case::iana_timezone(
+    r#"TZ="America/New_York" 1970-01-01 00:00"#,
+    "1970-01-01 00:00:00-05:00"
+)]
+// Bug #851934: timezone conversion case
+// Parse date in Australia/Perth (AWST, UTC+8) and output should reflect that timezone
+// Input: 2016-08-15 07:00 in Australia/Perth -> expected: 2016-08-15 07:00:00+08:00
+#[case::perth_to_london(
+    r#"TZ="Australia/Perth" 2016-08-15 07:00"#,
+    "2016-08-15 07:00:00+08:00"
+)]
+fn test_embedded_timezone(#[case] input: &str, #[case] expected: &str) {
+    check_absolute(input, expected);
+}