Delegating Switch not considered in Code Coverage

Question

I have found the following problem, while working with switch cases. R# showed me a simplification of the switch statement, which basically binds a delegate to the case label when you assign a variable.

var shape = shapeType switch
{
    ShapeType.Ellipse => new Ellipse(),
    ShapeType.Polygon => new Polygon(),
    _ => new Rectangle()
};

The benefit of this is readability for huge switch cases, because you basically save two thirds of the lines, for assigning switches.

My problem: I really like this type of switches, since it improves the readability, but this is not considered in the Code Coverage Tool of Visual Studio (VS Enterprise 2019 - 16.4.4). Since our policy strives towards a ~90% Code Coverage, each percent is valuable.

Is there a possibility to include these Switches in the Code Coverage?

Answer 1

Kate has a point here. My projects have a code coverage threshold of a hard 100%, and switch expressions are never completely covered, even if the equivalent switch statement is.

Here is an example:

The following switch statement provides 100% of code coverage in my project:

switch (values[3])
{
    case "F": return new string(Convert.ToString(value, 2).Reverse().ToArray()).PadRight(max, '0');
    case "G": return $"{value} of {max}";
    case "R" when value == 0: return $"none of {max}";
    case "R" when value == 1: return $"1st of {max}";
    case "R" when value == 2: return $"2nd of {max}";
    case "R" when value == 3: return $"3rd of {max}";
    default: return $"{value}th of {max}";
}

The equivalent switch expression gives only 99.91%, and the build on Jenkins fails:

return values[3] switch
{
    "F" => new string(Convert.ToString(value, 2).Reverse().ToArray()).PadRight(max, '0'),
    "G" => $"{value} of {max}",
    "R" when value == 0 => $"none of {max}",
    "R" when value == 1 => $"1st of {max}",
    "R" when value == 2 => $"2nd of {max}",
    "R" when value == 3 => $"3rd of {max}",
    _ => $"{value}th of {max}"
};

And the code coverage coloring does not indicate what branch is not being covered since it marks the whole statement.

I think this is a problem with how the compiler produces the final IL of the expression. It should be addressed as a C# bug and submitted to Microsoft to be fixed.