test(promql): add more test nh cases for fraction and trim

To be complete, add an empty NHCB to the minimal case.
For trim, add tests on empty histograms and test that show that
for non empty histograms
histogram_fraction(-Inf, x, h) * histogram_count(h) == h </ x
histogram_fraction(x, +Inf, h) * histogram_count(h) == h >/ x

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

promql/promqltest/testdata/native_histograms.test

@@ -1,24 +1,31 @@
-# Minimal valid case: an empty histogram.
+# Minimal valid case: an empty exponential or custom bucket histogram.
 load 5m
-	empty_histogram	{{}}
+	empty_histogram{h="exp"} {{}}
+	empty_histogram{h="cbh"} {{schema:-53 custom_values:[-2 3]}}
 
 eval instant at 1m empty_histogram
-	{__name__="empty_histogram"} {{}}
+	empty_histogram{h="exp"} {{}}
+	empty_histogram{h="cbh"} {{schema:-53 custom_values:[-2 3]}}
 
 eval instant at 1m histogram_count(empty_histogram)
-	{} 0
+	{h="exp"} 0
+	{h="cbh"} 0
 
 eval instant at 1m histogram_sum(empty_histogram)
-	{} 0
+	{h="exp"} 0
+	{h="cbh"} 0
 
 eval instant at 1m histogram_avg(empty_histogram)
-	{} NaN
+	{h="exp"} NaN
+	{h="cbh"} NaN
 
 eval instant at 1m histogram_fraction(-Inf, +Inf, empty_histogram)
-	{} NaN
+	{h="exp"} NaN
+	{h="cbh"} NaN
 
 eval instant at 1m histogram_fraction(0, 8, empty_histogram)
-	{} NaN
+	{h="exp"} NaN
+	{h="cbh"} NaN
 
 clear
 
@@ -2377,5 +2384,146 @@ eval instant at 1m cbh_for_join >/ on (label) float_for_join
   {label="a"} {{schema:-53 count:100.8 sum:502.4 custom_values:[5] buckets:[0.8 100]}}
   {label="b"} {{schema:-53 count:200.4 sum:1001.8 custom_values:[5] buckets:[0.4 200]}}
 
+load 1m
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+# Verify that trim of  empty histogram is empty, as opposed to NaN for histogram_fraction
+eval instant at 1m empty </ -Inf
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty </ -5
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty </ 0
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty </ 5
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty </ +Inf
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty >/ -Inf
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty >/ -5
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty >/ 0
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty >/ 5
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+eval instant at 1m empty >/ +Inf
+  empty{h="exp"} {{}}
+  empty{h="cbh"} {{schema:-53 custom_values:[-3 2]}}
+
+# Verify trim operators satisfy the identity for non-empty native histograms h:
+#   h </ x  == histogram_fraction(-Inf, x, h) * histogram_count(h)
+#   h >/ x  == histogram_fraction(x, +Inf, h) * histogram_count(h)
+# Each pair of eval statements tests both sides of the identity against the same
+# expected scalar.
+
+# Exponential histogram (schema:0, count:34), bucket boundary x=2.
+eval instant at 1m histogram_count(h_test </ 2)
+  {} 10
+
+eval instant at 1m histogram_fraction(-Inf, 2, h_test) * histogram_count(h_test)
+  {} 10
+
+eval instant at 1m histogram_count(h_test >/ 2)
+  {} 24
+
+eval instant at 1m histogram_fraction(2, +Inf, h_test) * histogram_count(h_test)
+  {} 24
+
+# Exponential histogram (schema:0, count:34), negative bucket boundary x=-1.
+eval instant at 1m histogram_count(h_test </ -1)
+  {} 2
+
+eval instant at 1m histogram_fraction(-Inf, -1, h_test) * histogram_count(h_test)
+  {} 2
+
+eval instant at 1m histogram_count(h_test >/ -1)
+  {} 32
+
+eval instant at 1m histogram_fraction(-1, +Inf, h_test) * histogram_count(h_test)
+  {} 32
+
+# Exponential histogram (schema:0, count:34), zero boundary x=0.
+eval instant at 1m histogram_count(h_test </ 0)
+  {} 3.5
+
+eval instant at 1m histogram_fraction(-Inf, 0, h_test) * histogram_count(h_test)
+  {} 3.5
+
+eval instant at 1m histogram_count(h_test >/ 0)
+  {} 30.5
+
+eval instant at 1m histogram_fraction(0, +Inf, h_test) * histogram_count(h_test)
+  {} 30.5
+
+# Exponential histogram (schema:0, count:34), interior point x=sqrt(2) (sub-bucket boundary).
+eval instant at 1m histogram_count(h_test </ 1.4142135624)
+  {} 8
+
+eval instant at 1m histogram_fraction(-Inf, 1.4142135624, h_test) * histogram_count(h_test)
+  {} 8
+
+eval instant at 1m histogram_count(h_test >/ 1.4142135624)
+  {} 26
+
+eval instant at 1m histogram_fraction(1.4142135624, +Inf, h_test) * histogram_count(h_test)
+  {} 26
+
+# Higher-resolution exponential histogram (schema:2, count:28), interior point x=1.13.
+eval instant at 1m histogram_count(h_test_2 </ 1.13)
+  {} 13.410582181123704
+
+eval instant at 1m histogram_fraction(-Inf, 1.13, h_test_2) * histogram_count(h_test_2)
+  {} 13.410582181123704
+
+eval instant at 1m histogram_count(h_test_2 >/ 1.13)
+  {} 14.589417818876296
+
+eval instant at 1m histogram_fraction(1.13, +Inf, h_test_2) * histogram_count(h_test_2)
+  {} 14.589417818876296
+
+# Custom-bucket histogram (count:15), bucket boundary x=15.
+eval instant at 1m histogram_count(cbh </ 15)
+  {} 11
+
+eval instant at 1m histogram_fraction(-Inf, 15, cbh) * histogram_count(cbh)
+  {} 11
+
+eval instant at 1m histogram_count(cbh >/ 15)
+  {} 4
+
+eval instant at 1m histogram_fraction(15, +Inf, cbh) * histogram_count(cbh)
+  {} 4
+
+# Custom-bucket histogram (count:15), interior point x=13 (linear interpolation).
+eval instant at 1m histogram_count(cbh </ 13)
+  {} 9.4
+
+eval instant at 1m histogram_fraction(-Inf, 13, cbh) * histogram_count(cbh)
+  {} 9.4
+
+eval instant at 1m histogram_count(cbh >/ 13)
+  {} 5.6
+
+eval instant at 1m histogram_fraction(13, +Inf, cbh) * histogram_count(cbh)
+  {} 5.6
 
 clear