Incorrect Code coverage reporting for C# Object Initializers

[serapqamar]

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!

[Youssef1313]

Moving the issue to code coverage.

cc @fhnaseer

[fhnaseer]

@serapqamar Can you please provide code for Example class as well? I am tried to mimic your code but getting full coverage.

[serapqamar]

Recent example where this occured:

The solution which fixed it:

[fhnaseer]

This is due to the conditional statement. If maybeNull is not null, then ?? notNull block is not executed and hence you will get partial coverage for it.