rework DOCKER_TEST_IMAGE parsing from review

.travis.yml

@@ -26,7 +26,7 @@ matrix:
       env:
         - TEST_BUILDS=1
         - MB_ML_VER=2010
-        - DOCKER_TEST_IMAGE=multibuild/xenial64
+        - DOCKER_TEST_IMAGE=multibuild/xenial_{PLAT}
     # 32-bit builds
     - os: linux
       dist: xenial
@@ -39,7 +39,7 @@ matrix:
         - TEST_BUILDS=1
         - PLAT=i686
         - MB_ML_VER=2010
-        - DOCKER_TEST_IMAGE=multibuild/bionic32
+        - DOCKER_TEST_IMAGE=multibuild/xenial_{PLAT}
     # Builds with caching
     - os: linux
       dist: xenial

README.rst

@@ -125,12 +125,18 @@ real ``build_wheel`` function, which now comes (by default) from
 Test phase
 ----------
 
-Specify the version to test with the ``DOCKER_TEST_IMAGE`` environment variable. The
-default version is ``matthewbrett/trusty:64``, or for ``i686`` platforms
-``matthewbrett/trusty:32``. Other versions that are currently valid are:
-
-* ``multibuild/bionic32`` (32 only)
-* ``multibuild/xenial64`` (64 only)
+Specify the version to test with the ``DOCKER_TEST_IMAGE`` environment
+variable. The default version is dependent on ``PLAT``:
+
+* ``matthewbrett/trusty:64``, for ``x86_64``
+* ``matthewbrett/trusty:32`` for ``i686``
+* ``multibuild/xenial_arm64v8`` for ``aarch64``
+* ``multibuild/xenial_ppc64le`` for ``ppc64le``
+* ``mutlibuild/xenial_s390x`` for ``s390x``
+
+Other valid values are any in https://hub.docker.com/orgs/multibuild/repositories,
+using the correct platform code. Alternatively, you can use the substitution
+pattern ``multibuild/xenial_{PLAT}`` in the ``.travis.yml`` file.
 
 See ``multibuild/docker_test_wrap.sh``.
 

travis_linux_steps.sh

@@ -121,12 +121,13 @@ function install_run {
     #  TEST_DEPENDS  (optional)
     #  MB_TEST_VER (optional)
     local plat=${1:-${PLAT:-x86_64}}
-    local mb_test_ver=${DOCKER_TEST_IMAGE:-"matthewbrett/trusty:"}
     if [ -z "$DOCKER_TEST_IMAGE" ]; then
         local bitness=$([ "$plat" == i686 ] && echo 32 || echo 64)
         local docker_image="matthewbrett/trusty:$bitness"
     else
-        local docker_image=$DOCKER_TEST_IMAGE
+        # aarch64 is called arm64v8 in Ubuntu
+        local plat_subst=$([ "$plat" == aarch64 ] && echo arm64v8 || echo $plat)
+        local docker_image="${DOCKER_TEST_IMAGE/\{plat_subst\}/$plat_subst}"
     fi
     docker pull $docker_image
     docker run --rm \