warn the users (once!) that if they run less than 15 iterations, the …

…MultimodalDistributionAnalyzer is not going to work, dotnet#763

src/BenchmarkDotNet/Analysers/Conclusion.cs

@@ -1,10 +1,11 @@
-using BenchmarkDotNet.Reports;
+using System;
+using BenchmarkDotNet.Reports;
 using JetBrains.Annotations;
 
 namespace BenchmarkDotNet.Analysers
 {
     // TODO: Find a better name
-    public sealed class Conclusion
+    public sealed class Conclusion : IEquatable<Conclusion>
     {
         [NotNull]
         public string AnalyserId { get; }
@@ -33,5 +34,34 @@ public static Conclusion CreateWarning(string analyserId, string message, [CanBe
 
         public static Conclusion CreateError(string analyserId, string message, [CanBeNull] BenchmarkReport report = null) 
             => new Conclusion(analyserId, ConclusionKind.Error, message, report);
+
+        public bool Equals(Conclusion other)
+        {
+            if (ReferenceEquals(null, other))
+                return false;
+            if (ReferenceEquals(this, other))
+                return true;
+            return string.Equals(AnalyserId, other.AnalyserId) && Kind == other.Kind && string.Equals(Message, other.Message);
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(null, obj))
+                return false;
+            if (ReferenceEquals(this, obj))
+                return true;
+            return obj is Conclusion && Equals((Conclusion) obj);
+        }
+
+        public override int GetHashCode()
+        {
+            unchecked
+            {
+                int hashCode = AnalyserId.GetHashCode();
+                hashCode = (hashCode * 397) ^ (int) Kind;
+                hashCode = (hashCode * 397) ^ Message.GetHashCode();
+                return hashCode;
+            }
+        }
     }
 }

src/BenchmarkDotNet/Analysers/MultimodalDistributionAnalyzer.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using BenchmarkDotNet.Engines;
 using BenchmarkDotNet.Mathematics;
 using BenchmarkDotNet.Reports;
 using JetBrains.Annotations;
@@ -7,20 +8,21 @@ namespace BenchmarkDotNet.Analysers
 {
     public class MultimodalDistributionAnalyzer : AnalyserBase
     {
-        public override string Id => "MultimodalDistribution";
         public static readonly IAnalyser Default = new MultimodalDistributionAnalyzer();
 
         private MultimodalDistributionAnalyzer() { }
 
-        [NotNull]
-        private Conclusion Create([NotNull] string kind, double mValue, [CanBeNull] BenchmarkReport report)
-            => CreateWarning($"It seems that the distribution {kind} (mValue = {mValue})", report);
+        public override string Id => "MultimodalDistribution";
 
         public override IEnumerable<Conclusion> AnalyseReport(BenchmarkReport report, Summary summary)
         {
             var statistics = report.ResultStatistics;
-            if (statistics == null || statistics.N < 15)
+            if (statistics == null)
                 yield break;
+            if (statistics.N < EngineResolver.DefaultMinTargetIterationCount)
+                yield return CreateHint($"The number of iterations was set to less than {EngineResolver.DefaultMinTargetIterationCount}, " +
+                                        $"{nameof(MultimodalDistributionAnalyzer)} needs at least {EngineResolver.DefaultMinTargetIterationCount} iterations to work."); 
+
             double mValue = MathHelper.CalculateMValue(statistics);
             if (mValue > 4.2)
                 yield return Create("is multimodal", mValue, report);
@@ -29,5 +31,9 @@ public override IEnumerable<Conclusion> AnalyseReport(BenchmarkReport report, Su
             else if (mValue > 2.8)
                 yield return Create("can have several modes", mValue, report);
         }
+
+        [NotNull]
+        private Conclusion Create([NotNull] string kind, double mValue, [CanBeNull] BenchmarkReport report)
+            => CreateWarning($"It seems that the distribution {kind} (mValue = {mValue})", report);
     }
 }

src/BenchmarkDotNet/Jobs/RunMode.cs

@@ -1,4 +1,5 @@
-using BenchmarkDotNet.Characteristics;
+using BenchmarkDotNet.Analysers;
+using BenchmarkDotNet.Characteristics;
 using BenchmarkDotNet.Engines;
 using BenchmarkDotNet.Horology;
 
@@ -136,7 +137,8 @@ public int UnrollFactor
 
         /// <summary>
         /// Minimum count of target iterations that should be performed
-        /// The default is 15
+        /// The default value is 15
+        /// <remarks>If you set this value to below 15, then <see cref="MultimodalDistributionAnalyzer"/> is not going to work</remarks>
         /// </summary>
         public int MinTargetIterationCount
         {
@@ -146,7 +148,8 @@ public int MinTargetIterationCount
 
         /// <summary>
         /// Maximum count of target iterations that should be performed
-        /// The default is 100 
+        /// The default value is 100
+        /// <remarks>If you set this value to below 15, then <see cref="MultimodalDistributionAnalyzer"/>  is not going to work</remarks>
         /// </summary>
         public int MaxTargetIterationCount
         {

src/BenchmarkDotNet/Running/BenchmarkRunner.cs

@@ -208,7 +208,7 @@ private static Summary Run(
             MarkdownExporter.Console.ExportToLog(summary, logger);
 
             // TODO: make exporter
-            ConclusionHelper.Print(logger, config.GetCompositeAnalyser().Analyse(summary).ToList());
+            ConclusionHelper.Print(logger, config.GetCompositeAnalyser().Analyse(summary).Distinct().ToList());
 
             // TODO: move to conclusions
             var columnWithLegends = summary.Table.Columns.Select(c => c.OriginalColumn).Where(c => !string.IsNullOrEmpty(c.Legend)).ToList();