[PSM Interop] Allow `dev` TESTING_VERSION that doesn't override images (#33062)

Resolve `TESTING_VERSION` to `dev-VERSION` when the job is initiated by
a user, and not the CI. Override this behavior with setting
`FORCE_TESTING_VERSION`.

This solves the problem with the manual job runs executed against a WIP
branch (f.e. a PR) overriding the tag of the CI-built image we use for
daily testing.

The `dev` and `dev-VERSION` "magic" values supported by the
`--testing_version` flag:

- `dev` and `dev-master` and treated as `master`: all
`config.version_gte` checks resolve to `True`.
- `dev-VERSION` is treated as `VERSION`: `dev-v1.55.x` is treated as
simply `v1.55.x`. We do this so that when manually running jobs for old
branches the feature skip check still works, and unsupported tests are
skipped.

This changes will take care of all langs/branches, no backports needed.

ref b/256845629

tools/internal_ci/linux/grpc_xds_k8s_install_test_driver.sh

@@ -23,6 +23,7 @@ readonly TEST_DRIVER_REPO_URL="https://github.com/${TEST_DRIVER_REPO_OWNER:-grpc
 readonly TEST_DRIVER_BRANCH="${TEST_DRIVER_BRANCH:-master}"
 readonly TEST_DRIVER_PATH="tools/run_tests/xds_k8s_test_driver"
 readonly TEST_DRIVER_PROTOS_PATH="src/proto/grpc/testing"
+readonly FORCE_TESTING_VERSION="${FORCE_TESTING_VERSION:-}"
 
 # GKE cluster identifiers.
 readonly GKE_CLUSTER_PSM_LB="psm-lb"
@@ -372,6 +373,46 @@ kokoro_setup_python_virtual_environment() {
   python3 -m pip --version
 }
 
+#######################################
+# Determines the version branch under test from Kokoro environment.
+# Globals:
+#   KOKORO_JOB_NAME
+#   KOKORO_BUILD_INITIATOR
+#   FORCE_TESTING_VERSION: Forces the testing version to be something else.
+#   TESTING_VERSION: Populated with the version branch under test,
+#                    f.e. master, dev, v1.42.x.
+# Outputs:
+#   Sets TESTING_VERSION global variable.
+#######################################
+kokoro_get_testing_version() {
+  # All grpc kokoro jobs names structured to have the version identifier in the third position:
+  # - grpc/core/master/linux/...
+  # - grpc/core/v1.42.x/branch/linux/...
+  # - grpc/java/v1.47.x/branch/...
+  # - grpc/go/v1.47.x/branch/...
+  # - grpc/node/v1.6.x/...
+  local version_from_job_name
+  version_from_job_name=$(echo "${KOKORO_JOB_NAME}" | cut -d '/' -f3)
+
+  if [[ -n "${FORCE_TESTING_VERSION}" ]]; then
+    # Allows to override the testing version, and force tagging the built
+    # images, if necessary.
+    readonly TESTING_VERSION="${FORCE_TESTING_VERSION}"
+  elif [[ "${KOKORO_BUILD_INITIATOR:-anonymous}" != "kokoro" ]]; then
+    # If not initiated by Kokoro, it's a dev branch.
+    # This allows to know later down the line that the built image doesn't need
+    # to be tagged, and avoid overriding an actual versioned image used in tests
+    # (e.g. v1.42.x, master) with a dev build.
+    if [[ -n "${version_from_job_name}" ]]; then
+      readonly TESTING_VERSION="dev-${version_from_job_name}"
+    else
+      readonly TESTING_VERSION="dev"
+    fi
+  else
+    readonly TESTING_VERSION="${version_from_job_name}"
+  fi
+}
+
 #######################################
 # Installs and configures the test driver on Kokoro VM.
 # Globals:
@@ -400,13 +441,8 @@ kokoro_setup_test_driver() {
   # Capture Kokoro VM version info in the log.
   kokoro_print_version
 
-  # All grpc kokoro jobs names structured to have the version identifier in the third position:
-  # - grpc/core/master/linux/...
-  # - grpc/core/v1.42.x/branch/linux/...
-  # - grpc/java/v1.47.x/branch/...
-  # - grpc/go/v1.47.x/branch/...
-  # - grpc/node/v1.6.x/...
-  readonly TESTING_VERSION=$(echo "${KOKORO_JOB_NAME}" | cut -d '/' -f3)
+  # Get testing version from the job name.
+  kokoro_get_testing_version
 
   # Kokoro clones repo to ${KOKORO_ARTIFACTS_DIR}/github/${GITHUB_REPOSITORY}
   local github_root="${KOKORO_ARTIFACTS_DIR}/github"
@@ -456,6 +492,13 @@ local_setup_test_driver() {
   readonly KUBE_CONTEXT="${KUBE_CONTEXT:-$(kubectl config current-context)}"
   readonly SECONDARY_KUBE_CONTEXT="${SECONDARY_KUBE_CONTEXT}"
 
+  # Never override docker image for local runs, unless explicitly forced.
+  if [[ -n "${FORCE_TESTING_VERSION}" ]]; then
+    readonly TESTING_VERSION="${FORCE_TESTING_VERSION}"
+  else
+    readonly TESTING_VERSION="dev"
+  fi
+
   local test_driver_repo_dir
   test_driver_repo_dir="${TEST_DRIVER_REPO_DIR:-$(mktemp -d)/${TEST_DRIVER_REPO_NAME}}"
   test_driver_install "${test_driver_repo_dir}"

tools/run_tests/xds_k8s_test_driver/framework/helpers/skips.py

@@ -57,16 +57,24 @@ class TestConfig:
     version: Optional[str]
 
     def version_gte(self, another: str) -> bool:
-        """Returns a bool for whether the version is >= another one.
+        """Returns a bool for whether this VERSION is >= then ANOTHER version.
 
-        A version is greater than or equal to another version means its version
-        number is greater than or equal to another version's number. Version
-        "master" is always considered latest.
-        E.g., master >= v1.41.x >= v1.40.x >= v1.9.x.
+        Special cases:
 
-        Unspecified version is treated as 'master', but isn't explicitly set.
+        1) Versions "master" or "dev" are always greater than ANOTHER:
+        - master > v1.999.x > v1.55.x
+        - dev > v1.999.x > v1.55.x
+        - dev == master
+
+        2) Versions "dev-VERSION" behave the same as the VERSION:
+        - dev-master > v1.999.x > v1.55.x
+        - dev-master == dev == master
+        - v1.55.x > dev-v1.54.x > v1.53.x
+        - dev-v1.54.x == v1.54.x
+
+        3) Unspecified version (self.version is None) is treated as "master".
         """
-        if self.version == 'master' or self.version is None:
+        if self.version in ('master', 'dev', 'dev-master', None):
             return True
         if another == 'master':
             return False
@@ -77,10 +85,13 @@ class TestConfig:
                 f"server_lang='{self.server_lang}', version={self.version!r})")
 
     @staticmethod
-    def _parse_version(s: str) -> pkg_version.Version:
-        if s.endswith(".x"):
-            s = s[:-2]
-        return pkg_version.Version(s)
+    def _parse_version(version: str) -> pkg_version.Version:
+        if version.startswith('dev-'):
+            # Treat "dev-VERSION" as "VERSION".
+            version = version[4:]
+        if version.endswith('.x'):
+            version = version[:-2]
+        return pkg_version.Version(version)
 
 
 def _get_lang(image_name: str) -> Lang:

tools/run_tests/xds_k8s_test_driver/framework/xds_flags.py

@@ -120,7 +120,7 @@ CLIENT_PORT = flags.DEFINE_integer(
 TESTING_VERSION = flags.DEFINE_string(
     "testing_version",
     default=None,
-    help="The testing gRPC version branch name. Like master, v1.41.x, v1.37.x")
+    help="The testing gRPC version branch name. Like master, dev, v1.55.x")
 
 FORCE_CLEANUP = flags.DEFINE_bool(
     "force_cleanup",