really add tests

test/CDB_StatsTest.sql

@@ -2,16 +2,12 @@
 -- http://mathworld.wolfram.com/UniformDistribution.html
 
 With dist As (
-  SELECT random() As val
+  SELECT random()::numeric As val
   FROM generate_series(1,5000000) t
-),
-m As (
-  SELECT avg(val) mn, count(*) cnt, stddev(val) s
-  FROM dist
-  )
+)
 
 SELECT 
-  abs(sum(power(mn - val,4)) / ( cnt * power(s,4)) - 3 + 1.20) < 1e-3 As kurtosis,
-  abs(sum(power(mn - val,3)) / ( cnt * power(s,3))) < 1e-3 As skewness
-FROM dist, m
-GROUP BY m.cnt, m.mn, m.s
+  -- does random dist values match within 1% of known values
+  abs(CDB_Kurtosis(array_agg(val)) + 1.20) < 1e-2 As kurtosis,
+  abs(CDB_Skewness(array_agg(val)) - 0) < 1e-2 As skewness
+FROM dist