added unit tests for bigint

tests/test_bigint.nim

@@ -0,0 +1,63 @@
+import mmath/bigint
+import unittest
+import random
+from strutils import parseBiggestUInt
+
+suite "Nim arbitrary precision integers (powered by GMP)":
+
+    let str = "2347822319"
+    test "parse " & str:
+        let str = "2347822319"
+        let bi = BigInt.fromString(str, 10)
+        let ul : BiggestUInt = parseBiggestUInt(str)
+        check newBigInt(ul.int64) == bi
+
+    var rng = initRand(101325)
+
+    for i in 0..5:
+        let n1 = rng.rand(-1000..1000).int64
+        let n2 = rng.rand(-1000..1000).int64
+        let bi1 = BigInt.of(n1)
+        let bi2 = BigInt.of(n2)
+
+        test $n1 & " + " & $n2:
+            check BigInt.of(n1 + n2) == bi1 + bi2
+
+        test $n1 & " - " & $n2:
+            check BigInt.of(n1 - n2) == bi1 - bi2
+
+        test $n1 & " * " & $n2:
+            check BigInt.of(n1 * n2) == bi1 * bi2
+
+        test $n1 & " div " & $n2:
+            check BigInt.of(n1 div n2) == bi1 div bi2
+
+        test $n1 & " mod " & $n2:
+            check BigInt.of(n1 mod n2) == bi1 mod bi2
+        
+        test $n1 & " pow " & $3:
+            check BigInt.of(n1 * n1 * n1) == pow(bi1, 3)
+
+        test "abs(" & $n1 & ")":
+            check BigInt.of(n1.abs()) == bi1.abs() 
+
+        test "abs(" & $n2 & ")":
+            check BigInt.of(n2.abs()) == bi2.abs() 
+
+        test $n1 & " cmp " & $n2:
+            check cmp(n1, n2) == cmp(bi1, bi2)
+
+        test $n1 & " < " & $n2:
+            check (n1 < n2) == (bi1 < bi2)
+
+        test $n1 & " > " & $n2:
+            check (n1 > n2) == (bi1 > bi2)
+
+        test $n1 & " == " & $n1:
+            check bi1 == bi1
+
+        test $n2 & " == " & $n2:
+            check bi2 == bi2
+
+        test $n1 & " != " & $n2:
+            check bi1 != bi2