package main

import (
    "testing"
    "log"
)

var mersennes = []int {
    2,
    3,
    5,
    7,
    13,
    17,
    19,
    31,
    61,
}

func TestPrimality(t *testing.T) {
    p := 0
    for i:= 2; i <= mersennes[len(mersennes) - 1]; i++ {
        log.Printf("isPrime(%d) -> [%t]\n", i, isPrime(i))
        if (mersennes[p] == i) {
            if !isPrime(i) {
                t.Errorf("[%d] should be calculated as prime", i)
            }
            p++
        } else {
            if isPrime(i) {
                t.Errorf("[%d] should be calculated as composite", i)
            }
        }
    }
}

package main

import (
    "testing"
)

var mersennes = []int {
    2,
    3,
    5,
    7,
    13,
    17,
    19,
    31,
    61,
}

func TestPrime(t *testing.T) {
    for _, p := range mersennes {
        if !isPrime(p) {
            t.Errorf("p=[%d] should be calculated as prime", p)

        }
    }
}

--- 
+++ 
@@ -2,6 +2,7 @@
 
 import (
     "testing"
+    "log"
 )
 
 var mersennes = []int {
@@ -16,11 +17,19 @@
     61,
 }
 
-func TestPrime(t *testing.T) {
-    for _, p := range mersennes {
-        if !isPrime(p) {
-            t.Errorf("p=[%d] should be calculated as prime", p)
-
+func TestPrimality(t *testing.T) {
+    p := 0
+    for i:= 2; i <= mersennes[len(mersennes) - 1]; i++ {
+        log.Printf("isPrime(%d) -> [%t]\n", i, isPrime(i))
+        if (mersennes[p] == i) {
+            if !isPrime(i) {
+                t.Errorf("[%d] should be calculated as prime", i)
+            }
+            p++
+        } else {
+            if isPrime(i) {
+                t.Errorf("[%d] should be calculated as composite", i)
+            }
         }
     }
 }
Update test to also check for composites
