crypto.rand: improve test to actually check for difference in data

vlib/crypto/rand/rand_test.v

@@ -5,9 +5,26 @@
 import crypto.rand
 
 fn test_crypto_rand() {
-	r := rand.read(100) or {
+	no_bytes := 100
+	max_percentage_diff := 20
+
+	r1 := rand.read(no_bytes) or {
 		assert false
 		return
 	}
-	assert r.len == 100
+	assert r1.len == no_bytes
+	r2 := rand.read(no_bytes) or {
+		assert false
+		return
+	}
+	assert r2.len == no_bytes
+	
+	mut difference := 0
+	for i, _ in r1 {
+		difference += if r1[i] == r2[i] {0} else {1}
+	}
+
+	diff_percentage := f32(100) - (f32(difference)/f32(no_bytes)*100)
+
+	assert diff_percentage <= max_percentage_diff
 }