Add circom test w/ circuit for CircomVerifierProof

Add circom test with circuit for CircomVerifierProofs, which allows to
automatically check that the data generated from arbo matches the circom
circuit of a SMTVerifierProof.
Added also GHA workflow to test the circuits with the output of arbo
code.

testvectors/circom/go-data-generator/generator_test.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"math/big"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+	"github.com/vocdoni/arbo"
+	"go.vocdoni.io/dvote/db"
+)
+
+func TestGenerator(t *testing.T) {
+	c := qt.New(t)
+	database, err := db.NewBadgerDB(c.TempDir())
+	c.Assert(err, qt.IsNil)
+	tree, err := arbo.NewTree(database, 4, arbo.HashFunctionPoseidon)
+	c.Assert(err, qt.IsNil)
+
+	bLen := tree.HashFunction().Len()
+
+	testVector := [][]int64{
+		{1, 11},
+		{2, 22},
+		{3, 33},
+		{4, 44},
+	}
+	for i := 0; i < len(testVector); i++ {
+		k := arbo.BigIntToBytes(bLen, big.NewInt(testVector[i][0]))
+		v := arbo.BigIntToBytes(bLen, big.NewInt(testVector[i][1]))
+		if err := tree.Add(k, v); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// proof of existence
+	k := arbo.BigIntToBytes(bLen, big.NewInt(int64(2)))
+	cvp, err := tree.GenerateCircomVerifierProof(k)
+	c.Assert(err, qt.IsNil)
+	jCvp, err := json.Marshal(cvp)
+	c.Assert(err, qt.IsNil)
+	// store the data into a file that will be used at the circom test
+	err = ioutil.WriteFile("go-smt-verifier-inputs.json", jCvp, 0600)
+	c.Assert(err, qt.IsNil)
+
+	// proof of non-existence
+	k = arbo.BigIntToBytes(bLen, big.NewInt(int64(5)))
+	cvp, err = tree.GenerateCircomVerifierProof(k)
+	c.Assert(err, qt.IsNil)
+	jCvp, err = json.Marshal(cvp)
+	c.Assert(err, qt.IsNil)
+	// store the data into a file that will be used at the circom test
+	err = ioutil.WriteFile("go-smt-verifier-non-existence-inputs.json", jCvp, 0600)
+	c.Assert(err, qt.IsNil)
+}