crypto: align file name with the VerificationMethod name

did_test.go

@@ -12,7 +12,7 @@ import (
 	_ "github.com/INFURA/go-did/methods/did-key"
 )
 
-func ExampleSignature() {
+func Example_signature() {
 	// errors need to be handled
 
 	// 1) Parse the DID string into a DID object
@@ -32,7 +32,7 @@ func ExampleSignature() {
 	// Output: Signature is valid, verified with method: Ed25519VerificationKey2020 did:key:z6MknwcywUtTy2ADJQ8FH1GcSySKPyKDmyzT4rPEE84XREse#z6MknwcywUtTy2ADJQ8FH1GcSySKPyKDmyzT4rPEE84XREse
 }
 
-func ExampleKeyAgreement() {
+func Example_keyAgreement() {
 	// errors need to be handled
 
 	// 1) We have a private key for Alice

methods/did-key/key.go

@@ -122,7 +122,7 @@ func (d DidKey) Document(opts ...did.ResolutionOption) (did.Document, error) {
 			jwk := jsonwebkey.NewJsonWebKey2020(mainVmId, pub, d)
 			doc.signature = jwk
 			doc.keyAgreement = jwk
-		case params.HasVerificationMethodHint(secp256k1vm.Type):
+		case params.HasVerificationMethodHint(secp256k1vm.Type2019):
 			vm := secp256k1vm.NewVerificationKey2019(mainVmId, pub, d)
 			doc.signature = vm
 			doc.keyAgreement = vm

methods/did-key/testvectors/vectors.go

@@ -183,7 +183,7 @@ func LoadTestVectors(filename string) ([]Vector, error) {
 			}
 
 			switch vmType {
-			case secp256k1vm.Type:
+			case secp256k1vm.Type2019:
 				vect.Pub, err = secp256k1.PublicKeyFromBytes(pubBytes)
 				if err != nil {
 					return nil, err

verifications/json.go

@@ -31,7 +31,7 @@ func UnmarshalJSON(data []byte) (did.VerificationMethod, error) {
 		res = &multikey.MultiKey{}
 	case p256vm.Type2021:
 		res = &p256vm.Key2021{}
-	case secp256k1vm.Type:
+	case secp256k1vm.Type2019:
 		res = &secp256k1vm.VerificationKey2019{}
 	case x25519vm.Type2019:
 		res = &x25519vm.KeyAgreementKey2019{}

verifications/secp256k1/VerificationKey2019.go

@@ -16,7 +16,7 @@ import (
 
 const (
 	JsonLdContext = "https://w3id.org/security/suites/secp256k1-2019/v1"
-	Type          = "EcdsaSecp256k1VerificationKey2019"
+	Type2019      = "EcdsaSecp256k1VerificationKey2019"
 )
 
 var _ did.VerificationMethodSignature = &VerificationKey2019{}
@@ -90,7 +90,7 @@ func (vm VerificationKey2019) ID() string {
 }
 
 func (vm VerificationKey2019) Type() string {
-	return Type
+	return Type2019
 }
 
 func (vm VerificationKey2019) Controller() string {