prow.sh: different E2E suite depending on Kubernetes version

Instead of always using the latest E2E tests for all Kubernetes
versions, the plan now is to use the tests that match the Kubernetes
version. However, for 1.13 we have to make an exception because the
suite for that version did not support the necessary
--storage.testdriver parameter.

prow.sh

@@ -52,6 +52,19 @@ configvar () {
     eval echo "\$3:" "$1=\${$1}"
 }
 
+# Prints the value of a variable + version suffix, falling back to variable + "LATEST".
+get_versioned_variable () {
+    local var="$1"
+    local version="$2"
+    local value
+
+    eval value="\${${var}_${version}}"
+    if ! [ "$value" ]; then
+        eval value="\${${var}_LATEST}"
+    fi
+    echo "$value"
+}
+
 # Go versions can be specified seperately for different tasks
 # If the pre-installed Go is missing or a different
 # version, the required version here will get installed
@@ -158,9 +171,15 @@ configvar CSI_PROW_HOSTPATH_CANARY "" "hostpath image"
 # all generated files are present.
 #
 # CSI_PROW_E2E_REPO=none disables E2E testing.
-configvar CSI_PROW_E2E_VERSION v1.14.0 "E2E version"
-configvar CSI_PROW_E2E_REPO https://github.com/kubernetes/kubernetes "E2E repo"
-configvar CSI_PROW_E2E_IMPORT_PATH k8s.io/kubernetes "E2E package"
+configvar CSI_PROW_E2E_VERSION_1_13 v1.14.0 "E2E version for Kubernetes 1.13.x" # we can't use the one from 1.13.x because it didn't have --storage.testdriver
+configvar CSI_PROW_E2E_VERSION_1_14 v1.14.0 "E2E version for Kubernetes 1.14.x"
+# TODO: add new CSI_PROW_E2E_VERSION entry for future Kubernetes releases
+configvar CSI_PROW_E2E_VERSION_LATEST master "E2E version for Kubernetes master" # testing against Kubernetes master is already tracking a moving target, so we might as well use a moving E2E version
+configvar CSI_PROW_E2E_REPO_LATEST https://github.com/kubernetes/kubernetes "E2E repo for Kubernetes >= 1.13.x" # currently the same for all versions
+configvar CSI_PROW_E2E_IMPORT_PATH_LATEST k8s.io/kubernetes "E2E package for Kubernetes >= 1.13.x" # currently the same for all versions
+configvar CSI_PROW_E2E_VERSION "$(get_versioned_variable CSI_PROW_E2E_VERSION "${csi_prow_kubernetes_version_suffix}")"  "E2E version"
+configvar CSI_PROW_E2E_REPO "$(get_versioned_variable CSI_PROW_E2E_REPO "${csi_prow_kubernetes_version_suffix}")" "E2E repo"
+configvar CSI_PROW_E2E_IMPORT_PATH "$(get_versioned_variable CSI_PROW_E2E_IMPORT_PATH "${csi_prow_kubernetes_version_suffix}")" "E2E package"
 
 # csi-sanity testing from the csi-test repo can be run against the installed
 # CSI driver. For this to work, deploying the driver must expose the Unix domain
@@ -200,42 +219,22 @@ regex_join () {
     echo "$@" | sed -e 's/  */|/g' -e 's/^|*//' -e 's/|*$//' -e 's/^$/this-matches-nothing/g'
 }
 
-# Prints the value of a variable + version suffix, falling back to variable + "LATEST".
-get_versioned_variable () {
-    local var="$1"
-    local version="$2"
-    local value
-
-    eval value="\${${var}_${version}}"
-    if ! [ "$value" ]; then
-        eval value="\${${var}_LATEST}"
-    fi
-    echo "$value"
-}
-
-# Which tests are alpha depends on the Kubernetes version. The same
-# E2E test suite is used for all Kubernetes versions, including older
-# Kubernetes.
-#
-# Feature tags in the test are set based on what is an alpha
-# feature in the Kubernetes version that contains the E2E test suite's
-# source code.
+# Which tests are alpha depends on the Kubernetes version. We could
+# use the same E2E test for all Kubernetes version. This would have
+# the advantage that new tests can be applied to older versions
+# without having to backport tests.
 #
-# So when testing against an older Kubernetes release, some tests
-# might be enabled by default which don't pass for that older
-# Kubernetes version. In that case, the
-# CSI_PROW_E2E_ALPHA_<k8s-version> variable cannot just
-# be based on the `Feature` tag, it also must contain the names
-# of tests that used to be alpha but no longer have that tag.
+# But the feature tag gets removed from E2E tests when the corresponding
+# feature becomes beta, so we would have to track which tests were
+# alpha in previous Kubernetes releases. This was considered too
+# error prone. Therefore we use E2E tests that match the Kubernetes
+# version that is getting tested.
 #
-# <k8s-version> is just major+minor version separated by
-# underscore. "latest" matches master. It is also used for
-# unknown versions, so when master gets released there is
-# no need to add a new versioned variable. That only needs to be
-# done when updating something in the configuration that leads
-# to "latest" no longer being suitable.
+# However, for 1.13.x testing we have to use the E2E tests from 1.14
+# because 1.13 didn't have --storage.testdriver yet, so for that (and only
+# that version) we have to define alpha tests differently.
 configvar CSI_PROW_E2E_ALPHA_1_13 '\[Feature: \[Testpattern:.Dynamic.PV..block.volmode.\] should.create.and.delete.block.persistent.volumes' "alpha tests for Kubernetes 1.13" # Raw block was an alpha feature in 1.13.
-configvar CSI_PROW_E2E_ALPHA_LATEST '\[Feature:' "alpha tests for Kubernetes master"
+configvar CSI_PROW_E2E_ALPHA_LATEST '\[Feature:' "alpha tests for Kubernetes >= 1.14" # there's no need to update this, adding a new case for CSI_PROW_E2E for a new Kubernetes is enough
 configvar CSI_PROW_E2E_ALPHA "$(get_versioned_variable CSI_PROW_E2E_ALPHA "${csi_prow_kubernetes_version_suffix}")" "alpha tests"
 
 # After the parallel E2E test without alpha features, a test cluster
@@ -251,6 +250,7 @@ configvar CSI_PROW_E2E_ALPHA "$(get_versioned_variable CSI_PROW_E2E_ALPHA "${csi
 # the failing test for "latest" or by updating the test and not running
 # it anymore for older releases.
 configvar CSI_PROW_E2E_ALPHA_GATES_1_13 'VolumeSnapshotDataSource=true,BlockVolume=true,CSIBlockVolume=true' "alpha feature gates for Kubernetes 1.13"
+# TODO: add new CSI_PROW_ALPHA_GATES entry for future Kubernetes releases
 configvar CSI_PROW_E2E_ALPHA_GATES_LATEST 'VolumeSnapshotDataSource=true' "alpha feature gates for latest Kubernetes"
 configvar CSI_PROW_E2E_ALPHA_GATES "$(get_versioned_variable CSI_PROW_E2E_ALPHA_GATES "${csi_prow_kubernetes_version_suffix}")" "alpha E2E feature gates"