sql: enable shared-process mode tenant testing for TestUnsplitRanges

I opened issue #142388 to track the work for enabling external-process mode
testing, as it turned out to be a non-trivial effort.

Author: shubhamdhama

pkg/base/test_server_args.go

@@ -519,6 +519,34 @@ func TestIsForStuffThatShouldWorkWithSharedProcessModeButDoesntYet(
 	}
 }
 
+// TestSkippedForExternalModeDueToPerformance can be used to disable selecting
+// the external process virtual cluster due to significant performance
+// degradation compared to other modes. However, the goal is to eventually make
+// it work efficiently in external mode.
+//
+// It should link to a github issue with label C-investigation.
+func TestSkippedForExternalModeDueToPerformance(issueNumber int) DefaultTestTenantOptions {
+	return testSkippedForExternalProcessMode(issueNumber)
+}
+
+// TestDoesNotWorkWithExternalProcessMode disables selecting the external
+// process virtual cluster for tests that are not functional in that mode and
+// require further investigation. Any test using this function should reference
+// a GitHub issue tagged with "C-investigation" describing the underlying
+// problem.
+func TestDoesNotWorkWithExternalProcessMode(issueNumber int) DefaultTestTenantOptions {
+	return testSkippedForExternalProcessMode(issueNumber)
+}
+
+func testSkippedForExternalProcessMode(issueNumber int) DefaultTestTenantOptions {
+	return DefaultTestTenantOptions{
+		testBehavior:           ttSharedProcess,
+		allowAdditionalTenants: true,
+		issueNum:               issueNumber,
+		label:                  "C-investigation",
+	}
+}
+
 // InternalNonDefaultDecision builds a sentinel value used inside a
 // mechanism in serverutils. Should not be used by tests directly.
 func InternalNonDefaultDecision(

pkg/sql/unsplit_range_test.go

@@ -12,6 +12,7 @@ import (
 	"errors"
 	"testing"
 
+	"github.com/cockroachdb/cockroach/pkg/base"
 	"github.com/cockroachdb/cockroach/pkg/jobs"
 	"github.com/cockroachdb/cockroach/pkg/keys"
 	"github.com/cockroachdb/cockroach/pkg/kv"
@@ -269,7 +270,8 @@ func TestUnsplitRanges(t *testing.T) {
 
 	ctx := context.Background()
 	run := func(t *testing.T, tc testCase) {
-		params, _ := createTestServerParams()
+		params, _ := createTestServerParamsAllowTenants()
+		params.DefaultTestTenant = base.TestDoesNotWorkWithExternalProcessMode(142388)
 		params.Knobs.JobsTestingKnobs = jobs.NewTestingKnobsWithShortIntervals()
 		params.Knobs.GCJob = &sql.GCJobTestingKnobs{
 			SkipWaitingForMVCCGC: true,