Test suite memory leak?

While attempting to run the tests with Python 3.7 there seem to be a memory leak. I did not have the issue on Python 2.7.

Installing collected packages: pytest-xdist
Successfully installed pytest-xdist-1.28.0
/build/pytest-xdist-1.28.0
post-installation fixup
shrinking RPATHs of ELF executables and libraries in /nix/store/qpma67a2xwsf489sr5agzh55zmp83q9r-python3.7-pytest-xdist-1.28.0
strip is /nix/store/kj9ynabqbdba10632p8yp13910bflzr6-binutils-2.31.1/bin/strip
stripping (with command strip and flags -S) in /nix/store/qpma67a2xwsf489sr5agzh55zmp83q9r-python3.7-pytest-xdist-1.28.0/lib
patching script interpreter paths in /nix/store/qpma67a2xwsf489sr5agzh55zmp83q9r-python3.7-pytest-xdist-1.28.0
checking for references to /build/ in /nix/store/qpma67a2xwsf489sr5agzh55zmp83q9r-python3.7-pytest-xdist-1.28.0...
running install tests
============================= test session starts ==============================
platform linux -- Python 3.7.4, pytest-5.1.0, py-1.8.0, pluggy-0.12.0
rootdir: /build/pytest-xdist-1.28.0, inifile: tox.ini, testpaths: testing
plugins: xdist-1.28.0, forked-1.0.2
collected 148 items / 5 deselected / 143 selected

Dependencies in Nix:

    "inputDrvs": {
      "/nix/store/2m2isdn9s0x6ybf7j7sm9h87ba8z62yc-python3.7-six-1.12.0.drv": [
        "out"
      ],
      "/nix/store/37bl2ylsycnyp4a0kmxf11zhylyxbk8d-python3.7-execnet-1.7.0.drv": [
        "out"
      ],
      "/nix/store/4i60rs5jq781b5qclcfdz81l0rg49xkq-python3-3.7.4.drv": [
        "out"
      ],
      "/nix/store/72y5wq26g3alkplr29hpamfn27g9lcmr-pytest-xdist-1.28.0.tar.gz.drv": [
        "out"
      ],
      "/nix/store/9fwyivx1w7dblc711qwg2hp34m2q3l9k-hook.drv": [
        "out"
      ],
      "/nix/store/gdp7vz51myy3l3mikkq9887ni9d5888m-python3.7-setuptools-41.0.1.drv": [
        "out"
      ],
      "/nix/store/h3vr9yv5k86glxi62k3pmqpybfrp0588-python3.7-pytest-5.1.0.drv": [
        "out"
      ],
      "/nix/store/kc20g0hvialmpkdb4zq8axwl3c7dd1xp-python3.7-pytest-forked-1.0.2.drv": [
        "out"
      ],
      "/nix/store/qglg08n0vnrk6n2abgwkx8k3qf91pjxs-hook.drv": [
        "out"
      ],
      "/nix/store/rdv9fzmp5mmnjyn5qnx8sp09ij754jix-bash-4.4-p23.drv": [
        "out"
      ],
      "/nix/store/rfc3lfprjylr77ikb195gi0gi1hs4128-python3.7-filelock-3.0.12.drv": [
        "out"
      ],
      "/nix/store/vgqg7ccdfr4mj8l0al6lr2b0b6pxlbks-python3.7-bootstrapped-pip-19.1.1.drv": [
        "out"
      ],
      "/nix/store/whw4llh6r16xsn4648g2k9xb250ksm83-python3.7-setuptools_scm-3.2.0.drv": [
        "out"
      ],
      "/nix/store/z7vng602pfq5pr4mg5pjvjr3d1y55h5g-stdenv-linux.drv": [
        "out"
      ]
    },

Start by reproducing the reported test run with Python 3.7, pytest 5.1.0, and pytest-xdist 1.28.0, then compare it with Python 2.7 using the 143 selected tests. The report does not name a source file or failing test; done requires isolating a reproducible leak and defining its scope before a fix can be assessed.