Support running test environments in parallel with `detox`

This patch namespaces the test temp directory and the output
coverage report file with the name of the environment under test,
such that separately run tests do not access the same files.

When running tests without tox, directly through setup.py,
then the tmp directory will still be `./tmp`.

  * .gitignore: Added new .coverage-reports/ directory

  * .gitlab-ci.yml: Rely on tox to combine and report coverage, only
    tell tox about the COVERAGE_PREFIX so that results can be namespaced
    by CI job name.

    This change also publishes the sources and final combined `.coverage`
    file in an output gitlab artifact for inspection, and lists some missing
    dependencies to the `coverage` job.

  * tox.ini: Add comments and refactor main [testenv] section so that
    other environments dont inherit too much unrelated cruft.

    Generate the coverate reports in the respective {envtmpdir} so that
    all per-process coverage files are prefixed with a full path, ensuring
    that concurrent runs don't mix reports and addressing concerns
    raised in #844.

    Also implemented new `tox -e coverage` environment to combine
    any found coverage and print a report.

  * .coveragerc: Omit .tox/ directory from coverage stats

Fixes issue #844

4 files changed, 56 insertions, 19 deletions

diff --git a/.coveragerc b/.coveragerc
index d81aec1a2..af22a1282 100644
--- a/.coveragerc
+++ b/.coveragerc
@@ -9,6 +9,8 @@ omit =
   # Omit generated code
   */buildstream/_protos/*
   */.eggs/*
+  # Omit .tox directory
+  */.tox/*
 
 [report]
 show_missing = True
diff --git a/.gitignore b/.gitignore
index 3fd1addbc..00cb4e2c4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,11 +13,12 @@ tests/**/*.pyc
 integration-cache/
 tmp
 .coverage
+.coverage-reports/
 .coverage.*
 .cache
 .pytest_cache/
 *.bst/
-.tox
+.tox/
 
 # Pycache, in case buildstream is ran directly from within the source
 # tree
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 9706037a4..78e725da8 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -13,6 +13,7 @@ variables:
   PYTEST_ADDOPTS: "--color=yes"
   INTEGRATION_CACHE: "${CI_PROJECT_DIR}/cache/integration-cache"
   TEST_COMMAND: "tox -- --color=yes --integration"
+  COVERAGE_PREFIX: "${CI_JOB_NAME}."
 
 
 #####################################################
@@ -24,9 +25,6 @@ variables:
 .tests-template: &tests
   stage: test
 
-  variables:
-    COVERAGE_DIR: coverage-linux
-
   before_script:
   # Diagnostics
   - mount
@@ -40,14 +38,11 @@ variables:
   - su buildstream -c "${TEST_COMMAND}"
 
   after_script:
-  # Collect our reports
-  - mkdir -p ${COVERAGE_DIR}
-  - cp .coverage ${COVERAGE_DIR}/coverage."${CI_JOB_NAME}"
   except:
   - schedules
   artifacts:
     paths:
-    - ${COVERAGE_DIR}
+    - .coverage-reports
 
 tests-debian-9:
   image: buildstream/testsuite-debian:9-5da27168-32c47d1c
@@ -83,7 +78,6 @@ tests-unix:
   <<: *tests
   variables:
     BST_FORCE_BACKEND: "unix"
-    COVERAGE_DIR: coverage-unix
 
   script:
 
@@ -239,22 +233,22 @@ coverage:
   stage: post
   coverage: '/TOTAL +\d+ +\d+ +(\d+\.\d+)%/'
   script:
-    - pip3 install -r requirements/requirements.txt -r requirements/dev-requirements.txt
-    - pip3 install --no-index .
-    - mkdir report
-    - cd report
-    - cp ../coverage-unix/coverage.* .
-    - cp ../coverage-linux/coverage.* .
-    - ls coverage.*
-    - coverage combine --rcfile=../.coveragerc -a coverage.*
-    - coverage report --rcfile=../.coveragerc -m
+    - cp -a .coverage-reports/ ./coverage-sources
+    - tox -e coverage
+    - cp -a .coverage-reports/ ./coverage-report
   dependencies:
   - tests-debian-9
   - tests-fedora-27
   - tests-fedora-28
+  - tests-fedora-missing-deps
+  - tests-ubuntu-18.04
   - tests-unix
   except:
   - schedules
+  artifacts:
+    paths:
+    - coverage-sources/
+    - coverage-report/
 
 # Deploy, only for merges which land on master branch.
 #
diff --git a/tox.ini b/tox.ini
index 3b6496d3f..abc13d03a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,9 +1,20 @@
+#
+# Tox global configuration
+#
 [tox]
 envlist = py35,py36,py37
 skip_missing_interpreters = true
 
+#
+# Defaults for all environments
+#
+# Anything specified here is iherited by the sections
+#
 [testenv]
-commands = pytest {posargs}
+commands =
+    pytest --basetemp {envtmpdir} {posargs}
+    mkdir -p .coverage-reports
+    mv {envtmpdir}/.coverage {toxinidir}/.coverage-reports/.coverage.{env:COVERAGE_PREFIX:}{envname}
 deps =
     -rrequirements/requirements.txt
     -rrequirements/dev-requirements.txt
@@ -13,6 +24,32 @@ passenv =
     GI_TYPELIB_PATH
     INTEGRATION_CACHE
 
+#
+# These keys are not inherited by any other sections
+#
+setenv =
+    py{35,36,37}: COVERAGE_FILE = {envtmpdir}/.coverage
+whitelist_externals =
+    py{35,36,37}:
+        mv
+        mkdir
+
+#
+# Coverage reporting
+#
+[testenv:coverage]
+commands =
+    - coverage combine --rcfile={toxinidir}/.coveragerc {toxinidir}/.coverage-reports/
+    coverage report --rcfile={toxinidir}/.coveragerc -m
+deps =
+    -rrequirements/requirements.txt
+    -rrequirements/dev-requirements.txt
+setenv =
+    COVERAGE_FILE = {toxinidir}/.coverage-reports/.coverage
+
+#
+# Running linters
+#
 [testenv:lint]
 commands =
     pycodestyle
@@ -22,6 +59,9 @@ deps =
     -rrequirements/dev-requirements.txt
     -rrequirements/plugin-requirements.txt
 
+#
+# Building documentation
+#
 [testenv:docs]
 commands =
     make -C doc