Test coverage gap when using defstruct

[liamwhite]

Elixir and Erlang/OTP versions

Erlang/OTP 27 [erts-15.0] [source] [64-bit] [smp:32:32] [ds:32:32:10] [async-threads:1] [jit:ns]

Elixir 1.17.0 (compiled with Erlang/OTP 27)

Operating system

Linux

Current behavior

After creating a project structure with the following files:

# mix new coverage && cd coverage

# cat > lib/coverage.ex 
defmodule Coverage do
  defstruct x: %{},
            y: %{},
            z: %{}

  def new(opts) do
    struct!(__MODULE__, opts)
  end
end

# cat > test/coverage_test.exs
defmodule CoverageTest do
  use ExUnit.Case

  test "exercises all functionality" do
    assert %{} = Coverage.new(x: "x", y: "y", z: "z")
  end
end

running mix test --cover produces a report where only 50% of the module has coverage:

Percentage | Module
-----------|--------------------------
    50.00% | Coverage
-----------|--------------------------
    50.00% | Total

However, every executable line contained in this file was executed. In the HTML report, one can observe that this is caused by the defstruct line, presumably due to the two clauses of the __struct__ function:

Expected behavior

This test run should have 100% coverage.

[Papipo]

Does the fix apply to defrecord? Because it has the same issue, I think.