False positive branch coverage

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#218 opened on Apr 22, 2026 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 66/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Quiet
Tech stack: csharp
Domain: testing-qa

Research direction

Start with MicrosoftCoverageTest.zip and run the shown dotnet test command against Class1.Test1. Compare the generated Cobertura report with the single executed path in the test; done means the report no longer marks both branch outcomes as covered for this reproduction.

Written by the indexing model from the issue text.

Description

Class under test

namespace CoverageTest;

public static class Class1
{
    public static int Test1(int n)
    {
        if (n < 10)
            n = Random.Shared.Next();
        return n;
    }
}

Test class

using Xunit;

namespace CoverageTest.Tests;

public static class Class1Tests
{
    [Fact]
    public static void Test1()
    {
        Class1.Test1(2);
    }
}

Command executed

dotnet test -verbosity:diagnostic -c Debug --collect:"Code Coverage;IncludeTestAssembly=False;Format=cobertura;CoverageFileName=R:\coverage\CoverageTest.Tests\cobertura.xml"

Excerpt from coverage results

<method line-rate="1" branch-rate="1" complexity="2" name="Test1" signature="(int)">
  <lines>
    <line number="6" hits="1" branch="False" />
    <line number="7" hits="1" branch="True" condition-coverage="100% (2/2)">
      <conditions>
        <condition number="0" type="jump" coverage="100%" />
      </conditions>
    </line>
    <line number="8" hits="1" branch="False" />
    <line number="9" hits="1" branch="False" />
    <line number="10" hits="1" branch="False" />
  </lines>
</method>

The branch is executed only once, so it should not be possible to have coverage of both sides of the branch (taken and not-taken).

MicrosoftCoverageTest.zip

Dominant language: C#
Stars: 125
Forks: 17
Avg merge: 1h 17m
Merged PRs (30d): 2

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