1 files changed, 112 insertions, 0 deletions
diff --git a/src/StardewModdingAPI.Tests/SDateTests.cs b/src/StardewModdingAPI.Tests/SDateTests.cs
new file mode 100644
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+++ b/src/StardewModdingAPI.Tests/SDateTests.cs
@@ -0,0 +1,112 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Text.RegularExpressions;
+using NUnit.Framework;
+using StardewModdingAPI.Utilities;
+
+namespace StardewModdingAPI.Tests
+{
+    /// <summary>Unit tests for <see cref="SDate"/>.</summary>
+    [TestFixture]
+    internal class SDateTests
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>All valid seasons.</summary>
+        private static string[] ValidSeasons = { "spring", "summer", "fall", "winter" };
+
+        /// <summary>All valid days of a month.</summary>
+        private static int[] ValidDays = Enumerable.Range(1, 28).ToArray();
+
+
+        /*********
+        ** Unit tests
+        *********/
+        /****
+        ** Constructor
+        ****/
+        [Test(Description = "Assert that the constructor sets the expected values for all valid dates.")]
+        public void Constructor_SetsExpectedValues([ValueSource(nameof(SDateTests.ValidSeasons))] string season, [ValueSource(nameof(SDateTests.ValidDays))] int day, [Values(1, 2, 100)] int year)
+        {
+            // act
+            SDate date = new SDate(day, season, year);
+
+            // assert
+            Assert.AreEqual(day, date.Day);
+            Assert.AreEqual(season, date.Season);
+            Assert.AreEqual(year, date.Year);
+        }
+
+        [Test(Description = "Assert that the constructor throws an exception if the values are invalid.")]
+        [TestCase(01, "Spring", 1)] // seasons are case-sensitive
+        [TestCase(01, "springs", 1)] // invalid season name
+        [TestCase(-1, "spring", 1)] // day < 0
+        [TestCase(29, "spring", 1)] // day > 28
+        [TestCase(01, "spring", -1)] // year < 1
+        [TestCase(01, "spring", 0)] // year < 1
+        [SuppressMessage("ReSharper", "AssignmentIsFullyDiscarded", Justification = "Deliberate for unit test.")]
+        public void Constructor_RejectsInvalidValues(int day, string season, int year)
+        {
+            // act & assert
+            Assert.Throws<ArgumentException>(() => _ = new SDate(day, season, year), "Constructing the invalid date didn't throw the expected exception.");
+        }
+
+        /****
+        ** ToString
+        ****/
+        [Test(Description = "Assert that ToString returns the expected string.")]
+        [TestCase("14 spring Y1", ExpectedResult = "14 spring Y1")]
+        [TestCase("01 summer Y16", ExpectedResult = "01 summer Y16")]
+        [TestCase("28 fall Y10", ExpectedResult = "28 fall Y10")]
+        [TestCase("01 winter Y1", ExpectedResult = "01 winter Y1")]
+        public string ToString(string dateStr)
+        {
+            return this.ParseDate(dateStr).ToString();
+        }
+
+        /****
+        ** AddDays
+        ****/
+        [Test(Description = "Assert that AddDays returns the expected date.")]
+        [TestCase("01 spring Y1", 15, ExpectedResult = "16 spring Y1")] // day transition
+        [TestCase("01 spring Y1", 28, ExpectedResult = "01 summer Y1")] // season transition
+        [TestCase("01 spring Y1", 28 * 4, ExpectedResult = "01 spring Y2")] // year transition
+        [TestCase("01 spring Y1", 28 * 7 + 17, ExpectedResult = "18 winter Y2")] // year transition
+        [TestCase("15 spring Y1", -14, ExpectedResult = "01 spring Y1")] // negative day transition
+        [TestCase("15 summer Y1", -28, ExpectedResult = "15 spring Y1")] // negative season transition
+        [TestCase("15 summer Y2", -28 * 4, ExpectedResult = "15 summer Y1")] // negative year transition
+        [TestCase("01 spring Y3", -(28 * 7 + 17), ExpectedResult = "12 spring Y1")] // negative year transition
+        public string AddDays(string dateStr, int addDays)
+        {
+            return this.ParseDate(dateStr).AddDays(addDays).ToString();
+        }
+
+
+        /*********
+        ** Private methods
+        *********/
+        /// <summary>Convert a string date into a game date, to make unit tests easier to read.</summary>
+        /// <param name="dateStr">The date string like "dd MMMM yy".</param>
+        private SDate ParseDate(string dateStr)
+        {
+            void Fail(string reason) => throw new AssertionException($"Couldn't parse date '{dateStr}' because {reason}.");
+
+            // parse
+            Match match = Regex.Match(dateStr, @"^(?<day>\d+) (?<season>\w+) Y(?<year>\d+)$");
+            if (!match.Success)
+                Fail("it doesn't match expected pattern (should be like 28 spring Y1)");
+
+            // extract parts
+            string season = match.Groups["season"].Value;
+            if (!int.TryParse(match.Groups["day"].Value, out int day))
+                Fail($"'{match.Groups["day"].Value}' couldn't be parsed as a day.");
+            if (!int.TryParse(match.Groups["year"].Value, out int year))
+                Fail($"'{match.Groups["year"].Value}' couldn't be parsed as a year.");
+
+            // build date
+            return new SDate(day, season, year);
+        }
+    }
+}