Add delta st inclusive test case for random vt

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>

tsdb/chunkenc/benchmark_test.go

@@ -139,7 +139,7 @@ func foreachFmtSampleCase(b *testing.B, fn func(b *testing.B, f fmtCase, s sampl
 			}(),
 		},
 		{
-			name: "vt=random steps/st=delta",
+			name: "vt=random steps/st=delta-exclusive",
 			samples: func() (ret []triple) {
 				t, v := initT, initV
 				for i := range nSamples {
@@ -151,6 +151,19 @@ func foreachFmtSampleCase(b *testing.B, fn func(b *testing.B, f fmtCase, s sampl
 				return ret
 			}(),
 		},
+		{
+			name: "vt=random steps/st=delta-inclusive",
+			samples: func() (ret []triple) {
+				t, v := initT, initV
+				for i := range nSamples {
+					st := t                    // ST is equal to the previous t.
+					t += rInts[i] - 50 + 15000 // 15 seconds +- up to 100ms of jitter.
+					v += rFloats[i] - 50       // Varying from -50 to +50 in 100 discrete steps.
+					ret = append(ret, triple{st: st, t: t, v: v})
+				}
+				return ret
+			}(),
+		},
 		{
 			name: "vt=random 0-1/st=0",
 			samples: func() (ret []triple) {