Tests for interval/checkpoint calculation

Author: nblumhardt

test/Serilog.Sinks.File.Tests/RollingIntervalExtensionsTests.cs

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+using System;
+using Xunit;
+
+namespace Serilog.Sinks.File.Tests
+{
+    public class RollingIntervalExtensionsTests
+    {
+        public static object[][] IntervalInstantCurrentNextCheckpoint => new[]
+        {
+            new object[]{ RollingInterval.Infinite, new DateTime(2018, 01, 01),           null, null },
+            new object[]{ RollingInterval.Year,     new DateTime(2018, 01, 01),           new DateTime(2018, 01, 01), new DateTime(2019, 01, 01) },
+            new object[]{ RollingInterval.Year,     new DateTime(2018, 06, 01),           new DateTime(2018, 01, 01), new DateTime(2019, 01, 01) },
+            new object[]{ RollingInterval.Month,    new DateTime(2018, 01, 01),           new DateTime(2018, 01, 01), new DateTime(2018, 02, 01) },
+            new object[]{ RollingInterval.Month,    new DateTime(2018, 01, 14),           new DateTime(2018, 01, 01), new DateTime(2018, 02, 01) },
+            new object[]{ RollingInterval.Day,      new DateTime(2018, 01, 01),           new DateTime(2018, 01, 01), new DateTime(2018, 01, 02) },
+            new object[]{ RollingInterval.Day,      new DateTime(2018, 01, 01, 12, 0, 0), new DateTime(2018, 01, 01), new DateTime(2018, 01, 02) },
+            new object[]{ RollingInterval.Hour,     new DateTime(2018, 01, 01, 0, 0, 0),  new DateTime(2018, 01, 01), new DateTime(2018, 01, 01, 1, 0, 0) },
+            new object[]{ RollingInterval.Hour,     new DateTime(2018, 01, 01, 0, 30, 0), new DateTime(2018, 01, 01), new DateTime(2018, 01, 01, 1, 0, 0) },
+            new object[]{ RollingInterval.Minute,   new DateTime(2018, 01, 01, 0, 0, 0),  new DateTime(2018, 01, 01), new DateTime(2018, 01, 01, 0, 1, 0) },
+            new object[]{ RollingInterval.Minute,   new DateTime(2018, 01, 01, 0, 0, 30), new DateTime(2018, 01, 01), new DateTime(2018, 01, 01, 0, 1, 0) }
+        };
+
+        [Theory]
+        [MemberData(nameof(IntervalInstantCurrentNextCheckpoint))]
+        public void NextIntervalTests(RollingInterval interval, DateTime instant, DateTime? currentCheckpoint, DateTime? nextCheckpoint)
+        {
+            var current = interval.GetCurrentCheckpoint(instant);
+            Assert.Equal(currentCheckpoint, current);
+
+            var next = interval.GetNextCheckpoint(instant);
+            Assert.Equal(nextCheckpoint, next);
+        }
+    }
+}