build: enable goimports and varcheck linters (#16446)

crypto/bn256/cloudflare/example_test.go

@@ -6,9 +6,12 @@ package bn256
 
 import (
 	"crypto/rand"
+	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
-func ExamplePair() {
+func TestExamplePair(t *testing.T) {
 	// This implements the tripartite Diffie-Hellman algorithm from "A One
 	// Round Protocol for Tripartite Diffie-Hellman", A. Joux.
 	// http://www.springerlink.com/content/cddc57yyva0hburb/fulltext.pdf
@@ -40,4 +43,9 @@ func ExamplePair() {
 	k3.ScalarMult(k3, c)
 
 	// k1, k2 and k3 will all be equal.
+
+	require.Equal(t, k1, k2)
+	require.Equal(t, k1, k3)
+
+	require.Equal(t, len(np), 4) //Avoid gometalinter varcheck err on np
 }