Revert "splitting tests"

This reverts commit ae49fde.

Author: asthamohta

.kokoro/build.sh

@@ -55,8 +55,6 @@ fi
 
 # If NOX_SESSION is set, it only runs the specified session,
 # otherwise run all the sessions.
-if [[ -n "${SPANNER_DATABASE_DIALECT:-}" ]]; then
-    export SPANNER_DATABASE_DIALECT = ${SPANNER_DATABASE_DIALECT:-}
 if [[ -n "${NOX_SESSION:-}" ]]; then
     python3 -m nox -s ${NOX_SESSION:-}
 else

.kokoro/presubmit/system-3.8-google-standard-sql.cfg

@@ -4,10 +4,4 @@
 env_vars: {
     key: "NOX_SESSION"
     value: "system-3.8"
-}
-
-# Run for postgres
-env_vars: {
-    key: "SPANNER_DATABASE_DIALECT"
-    value: "POSTGRESQL"
 }

.kokoro/presubmit/system-3.8-postgres.cfg .kokoro/presubmit/system-3.8.cfg.kokoro/presubmit/system-3.8-postgres.cfg renamed to .kokoro/presubmit/system-3.8.cfg

@@ -238,17 +238,15 @@ def install_systemtest_dependencies(session, *constraints):
 
 
 @nox.session(python=SYSTEM_TEST_PYTHON_VERSIONS)
-def system(session):
+@nox.parametrize("database_dialect", ["GOOGLE_STANDARD_SQL", "POSTGRESQL"])
+def system(session, database_dialect):
     """Run the system test suite."""
     constraints_path = str(
         CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
     )
     system_test_path = os.path.join("tests", "system.py")
     system_test_folder_path = os.path.join("tests", "system")
 
-    # If POSTGRESQL tests and Emulator, skip the tests
-    if os.environ.get("SPANNER_EMULATOR_HOST") and os.environ.get("SPANNER_DATABASE_DIALECT") == "POSTGRESQL":
-        session.skip("Postgresql is not supported by Emulator yet.")
     # Check the value of `RUN_SYSTEM_TESTS` env var. It defaults to true.
     if os.environ.get("RUN_SYSTEM_TESTS", "true") == "false":
         session.skip("RUN_SYSTEM_TESTS is set to false, skipping")
@@ -272,6 +270,10 @@ def system(session):
 
     install_systemtest_dependencies(session, "-c", constraints_path)
 
+    # If POSTGRESQL tests and Emulator, skip the tests
+    if os.environ.get("SPANNER_EMULATOR_HOST") and database_dialect == "POSTGRESQL":
+        session.skip("Postgresql is not supported by Emulator yet.")
+
     # Run py.test against the system tests.
     if system_test_exists:
         session.run(