microsoft / microsoft/codecoverage

Incorrect Code coverage reporting for C# Object Initializers

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Dominant language
C#
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Forks
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1h 17m
Merged PRs (30d)
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Description

We are running into an issue where code coverage reports incorrect or partial coverage for certain C# object/collection initializer patterns, even though the code path is fully executed.
Specifically, the following initializer-style pattern is not fully recognized by the coverage tool:

var thing = new Example
{
    name = "object one",
    [1] = '1',
    [2] = '4',
    [3] = '9',
    Size = Math.PI,
    ['C', 4] = "Middle C"
};

To investigate, I ran the impacted tests locally using two versions of vstest.console:
17.14.0-release-25203-01
18.0.1-release-25520-05
In both cases, the coverage results remained unchanged, which suggests this is not resolved by upgrading the test runner.

What we’ve observed is that rewriting the same logic using explicit assignments (instead of initializer-style patterns) results in correct coverage being reported. For example, the following pattern is correctly recognized by the coverage tool:

var thing = new Example();
thing.name = "object one";
thing[1] = '1';
thing[2] = '4';
thing[3] = '9';
thing.Size = Math.PI;
thing['C', 4] = "Middle C";

Based on this, it appears to be a limitation or bug in how the underlying coverage engine handles certain object/collection initializer patterns, rather than an issue with our pipeline or configuration.
If this is a known limitation, or if there is a recommended workaround or escalation path, guidance would be appreciated.
Thanks!

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Research direction

Start by reproducing the reported object and collection initializer pattern and its explicit-assignment equivalent with vstest.console 17.14.0-release-25203-01 and 18.0.1-release-25520-05. Compare the resulting coverage reports; done means the initializer statements are reported as covered when the code path is fully executed, or the limitation and workaround are documented.

Written by the indexing model from the issue text.

Assessment

Tech stack
csharp
Domain
testing-qa
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Needs clarification
Newbie friendliness
35/100

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