Add unit test for short number formatter

Author: drewgillies

src/NuGetGallery/ViewModels/StatisticsPackagesViewModel.cs

@@ -18,7 +18,7 @@ public enum WeekFormats
             YearWeekNumber
         }
 
-        private readonly string[] _magnitudeAbbreviations = new string[] { "", "k", "M", "B", "T", "q", "Q", "s", "S", "o", "n" };
+        private static readonly string[] _magnitudeAbbreviations = new string[] { "", "k", "M", "B", "T", "q", "Q", "s", "S", "o", "n" };
 
         private DateTime? _lastUpdatedUtc;
 
@@ -142,7 +142,9 @@ public string DisplayPercentage(float amount, float total)
             return (amount / total).ToString("P0", CultureInfo.CurrentCulture);
         }
 
-        public string DisplayShortNumber(double number, int sigFigures = 3)
+        public string DisplayShortNumber(double number) => DisplayShortNumber(number, sigFigures: 3);
+
+        internal static string DisplayShortNumber(double number, int sigFigures = 3)
         {
             var numDiv = 0;
 
@@ -152,7 +154,7 @@ public string DisplayShortNumber(double number, int sigFigures = 3)
                 numDiv++;
             }
 
-            // Find a rounding factor based on size, and round to sigFigures, e.g. for 3 sig figs, 1.774545 becomes 1.77.
+            // Find a rounding factor based on size, and round to sigFigures, e.g. for 3 sig figs, 1.776545 becomes 1.78.
             var placeValues = Math.Ceiling(Math.Log10(number));
             var roundingFactor = Math.Pow(10, sigFigures - placeValues);
             var roundedNum = Math.Round(number * roundingFactor) / roundingFactor;
@@ -169,7 +171,7 @@ public string DisplayShortNumber(double number, int sigFigures = 3)
 
             if (numDiv >= _magnitudeAbbreviations.Length)
             {
-                return formattedNum + $"10^{numDiv*3}";
+                return formattedNum + $" 10^{numDiv*3}";
             }
 
             return formattedNum + _magnitudeAbbreviations[numDiv];

tests/NuGetGallery.Facts/NuGetGallery.Facts.csproj

@@ -302,6 +302,7 @@
     <Compile Include="ViewModels\ListPackageItemRequiredSignerViewModelFacts.cs" />
     <Compile Include="ViewModels\ListPackageItemViewModelFacts.cs" />
     <Compile Include="ViewModels\PackageViewModelFacts.cs" />
+    <Compile Include="ViewModels\StatisticsPackagesViewModelFacts.cs" />
     <Compile Include="ViewModels\PreviousNextPagerViewModelFacts.cs" />
     <Compile Include="ViewModels\SignerViewModelFacts.cs" />
     <Compile Include="ViewModels\UserProfileModelFacts.cs" />

tests/NuGetGallery.Facts/ViewModels/StatisticsPackagesViewModelFacts.cs

@@ -0,0 +1,34 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Xunit;
+
+namespace NuGetGallery.ViewModels
+{
+    public class StatisticsPackagesViewModelFacts
+    {
+        [Theory]
+        [InlineData(1004856283, 3, "1.00B")]   // pad with trailing zeroes test
+        [InlineData(1403856283, 3, "1.40B")]   // pad with trailing zeroes test
+        [InlineData(1406856283, 3, "1.41B")]
+        [InlineData(1774856283, 3, "1.77B")]
+        [InlineData(1775856283, 3, "1.78B")]
+        [InlineData(1775856283, 5, "1.7759B")]
+        [InlineData(775856283, 3, "776M")]
+        [InlineData(775856283, 5, "775.86M")]
+        [InlineData(75856283, 3, "75.9M")]
+        [InlineData(56283, 3, "56.3k")]
+        [InlineData(56283283283283, 3, "56.3T")]
+        [InlineData(56283283283283283, 3, "56.3q")]
+        [InlineData(56283283283283283283283283283283d, 3, "56.3n")]
+        [InlineData(56283283283283283283283283283283283d, 3, "56.3 10^33")]
+        [InlineData(1, 3, "1.00")]
+        [InlineData(10, 3, "10.0")]
+        [InlineData(100, 3, "100")]
+        public void CreatesShortNumberRespectingSignificantFigures(double number, int sigFigs, string expected)
+        {
+            var result = StatisticsPackagesViewModel.DisplayShortNumber(number, sigFigs);
+            Assert.Equal(expected, result);
+        }
+    }
+}