Fix Duration.ToTimeSpan() inaccuracy rounding to millisecond (#1070)

Co-authored-by: Andreas Leeb <[email protected]>

Author: AndreasLeeb

UnitsNet.Tests/CustomCode/DurationTests.cs

@@ -63,6 +63,17 @@ public static void ToTimeSpanShouldNotThrowExceptionOnValuesSlightlySmallerThanT
             AssertEx.EqualTolerance(duration.Seconds, timeSpan.TotalSeconds, 1e-3);
         }
 
+        [Theory]
+        [InlineData(100, Units.DurationUnit.Nanosecond)]
+        [InlineData(1, Units.DurationUnit.Microsecond)]
+        [InlineData(1.234, Units.DurationUnit.Millisecond)]
+        public static void ToTimeSpanShouldNotRoundToMillisecond(double value, Units.DurationUnit unit)
+        {
+            Duration duration = Duration.From(value, unit);
+            TimeSpan timeSpan = duration.ToTimeSpan();
+            AssertEx.EqualTolerance(duration.Milliseconds, timeSpan.TotalMilliseconds, 1e-10);
+        }
+
         [Fact]
         public static void ExplicitCastToTimeSpanShouldReturnSameValue()
         {

UnitsNet.Tests/UnitsNet.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net5.0</TargetFrameworks>
+    <TargetFrameworks>net5.0;net48</TargetFrameworks>
     <RootNamespace>UnitsNet.Tests</RootNamespace>
     <LangVersion>latest</LangVersion>
     <IsTestProject>true</IsTestProject>

UnitsNet/CustomCode/Quantities/Duration.extra.cs

@@ -18,7 +18,7 @@ public TimeSpan ToTimeSpan()
             if ( Seconds > TimeSpan.MaxValue.TotalSeconds ||
                 Seconds < TimeSpan.MinValue.TotalSeconds )
                 throw new ArgumentOutOfRangeException( nameof( Duration ), "The duration is too large or small to fit in a TimeSpan" );
-            return TimeSpan.FromSeconds( Seconds );
+            return TimeSpan.FromTicks((long)(Seconds * TimeSpan.TicksPerSecond));
         }
 
         /// <summary>Get <see cref="DateTime"/> from <see cref="DateTime"/> plus <see cref="Duration"/>.</summary>