tenantcostclient: tighten query RU estimate test

The query RU estimate test involves two runs of test queries:
- via EXPLAIN ANALYZE to get the RU estimate
- "vanilla" way and getting the precise RU usage.

One of the test queries is a large INSERT, and previously we didn't
delete the data after the first run. As a result, the second run would
operate on 2x size of the data set. This commit fixes that oversight by
including a DELETE query into the test query set which allows us to
tighten the delta margin from 0.75 to 0.05 (got no failures in over 1k
runs with 0.05 now).

Release note: None

Author: yuzefovich

pkg/ccl/multitenantccl/tenantcostclient/query_ru_estimate_test.go

@@ -130,6 +130,10 @@ func TestEstimateQueryRUConsumption(t *testing.T) {
 			sql:   "SELECT 'deadbeef' FROM generate_series(1, 50000)",
 			count: 10,
 		},
+		{ // Delete (this also ensures that two runs work with the same dataset)
+			sql:   "DELETE FROM abcd WHERE true",
+			count: 1,
+		},
 	}
 
 	var err error
@@ -191,12 +195,7 @@ func TestEstimateQueryRUConsumption(t *testing.T) {
 	// Check the estimated RU aggregate for all the queries against the actual
 	// measured RU consumption for the tenant.
 	tenantMeasuredRUs = getTenantRUs() - tenantStartRUs
-	// Usually, the difference is within 0.25 delta, but in rare cases it can be
-	// outside of that delta (when ran on the gceworker, it was outside the 0.5
-	// delta within 6 minutes of stressing), so we allow for generous 0.75
-	// delta. This still provides a good enough sanity check for the RU
-	// estimation.
-	const deltaFraction = 0.75
+	const deltaFraction = 0.05
 	allowedDelta := tenantMeasuredRUs * deltaFraction
 	require.InDeltaf(t, tenantMeasuredRUs, tenantEstimatedRUs, allowedDelta,
 		"estimated RUs (%d) were not within %f RUs of the expected value (%f)",