Incorrect Code coverage reporting for C# Object Initializers

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#216 opened on Mar 31, 2026 9 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 4/5
Estimated time: 3-5 days
Newbie friendliness: 35/100

Issue type: Bug
Clarity: Needs clarification
Activity status: Quiet
Tech stack: csharp
Domain: testing-qa

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.

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!

Dominant language: C#
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