diff --git a/mjwt_test.go b/mjwt_test.go
index 3a83fe8..1c059eb 100644
--- a/mjwt_test.go
+++ b/mjwt_test.go
@@ -9,6 +9,8 @@ import (
 	"time"
 )
 
+var mt_ExtraKID = "tester"
+
 type testClaims struct{ TestValue string }
 
 func (t testClaims) Valid() error {
@@ -31,31 +33,111 @@ func (t testClaims2) Valid() error {
 
 func (t testClaims2) Type() string { return "testClaims2" }
 
+func setupTestKeyStoreMJWT(t *testing.T) (ks KeyStore, a, b, c *rsa.PrivateKey) {
+	ks = NewMJwtKeyStore()
+	var err error
+
+	a, err = rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	ks.SetKey("key1", a)
+
+	b, err = rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	ks.SetKey("key2", b)
+
+	c, err = rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	ks.SetKey("key3", c)
+
+	return
+}
+
 func TestExtractClaims(t *testing.T) {
 	t.Parallel()
-	key, err := rsa.GenerateKey(rand.Reader, 2048)
-	assert.NoError(t, err)
+	kStore, key, _, _ := setupTestKeyStoreMJWT(t)
 
-	s := NewMJwtSigner("mjwt.test", key)
-	token, err := s.GenerateJwt("1", "test", nil, 10*time.Minute, testClaims{TestValue: "hello"})
-	assert.NoError(t, err)
+	t.Run("TestNoKID", func(t *testing.T) {
+		t.Parallel()
+		s := NewMJwtSigner("mjwt.test", key)
+		token, err := s.GenerateJwt("1", "test", nil, 10*time.Minute, testClaims{TestValue: "hello"})
+		assert.NoError(t, err)
 
-	m := NewMJwtVerifier(&key.PublicKey)
-	_, _, err = ExtractClaims[testClaims](m, token)
-	assert.NoError(t, err)
+		m := NewMJwtVerifier(&key.PublicKey)
+		_, _, err = ExtractClaims[testClaims](m, token)
+		assert.NoError(t, err)
+	})
+
+	t.Run("TestKID", func(t *testing.T) {
+		t.Parallel()
+		s := NewMJwtSignerWithKeyStore("mjwt.test", key, kStore)
+		token1, err := s.GenerateJwt("1", "test", nil, 10*time.Minute, testClaims{TestValue: "hello"})
+		assert.NoError(t, err)
+		token2, err := s.GenerateJwtWithKID("1", "test", nil, 10*time.Minute, testClaims{TestValue: "hello"}, "key2")
+		assert.NoError(t, err)
+
+		m := NewMJwtVerifierWithKeyStore(&key.PublicKey, kStore)
+		_, _, err = ExtractClaims[testClaims](m, token1)
+		assert.NoError(t, err)
+		_, _, err = ExtractClaims[testClaims](m, token2)
+		assert.NoError(t, err)
+	})
 }
 
 func TestExtractClaimsFail(t *testing.T) {
 	t.Parallel()
-	key, err := rsa.GenerateKey(rand.Reader, 2048)
-	assert.NoError(t, err)
+	kStore, key, key2, _ := setupTestKeyStoreMJWT(t)
 
-	s := NewMJwtSigner("mjwt.test", key)
-	token, err := s.GenerateJwt("1", "test", nil, 10*time.Minute, testClaims{TestValue: "test"})
-	assert.NoError(t, err)
+	t.Run("TestInvalidClaims", func(t *testing.T) {
+		t.Parallel()
+		s := NewMJwtSigner("mjwt.test", key)
+		token, err := s.GenerateJwt("1", "test", nil, 10*time.Minute, testClaims{TestValue: "test"})
+		assert.NoError(t, err)
 
-	m := NewMJwtVerifier(&key.PublicKey)
-	_, _, err = ExtractClaims[testClaims2](m, token)
-	assert.Error(t, err)
-	assert.ErrorIs(t, err, ErrClaimTypeMismatch)
+		m := NewMJwtVerifier(&key.PublicKey)
+		_, _, err = ExtractClaims[testClaims2](m, token)
+		assert.Error(t, err)
+		assert.ErrorIs(t, err, ErrClaimTypeMismatch)
+	})
+
+	t.Run("TestDefaultKeyNoKID", func(t *testing.T) {
+		t.Parallel()
+		s := NewMJwtSignerWithKeyStore("mjwt.test", key, kStore)
+		token, err := s.GenerateJwtWithKID("1", "test", nil, 10*time.Minute, testClaims{TestValue: "test"}, "key1")
+		assert.NoError(t, err)
+
+		m := NewMJwtVerifier(&key.PublicKey)
+		_, _, err = ExtractClaims[testClaims](m, token)
+		assert.Error(t, err)
+		assert.ErrorIs(t, err, ErrNoPublicKeyFound)
+	})
+
+	t.Run("TestNoDefaultKey", func(t *testing.T) {
+		t.Parallel()
+		s := NewMJwtSignerWithKeyStore("mjwt.test", key, kStore)
+		token, err := s.GenerateJwt("1", "test", nil, 10*time.Minute, testClaims{TestValue: "test"})
+		assert.NoError(t, err)
+
+		m := NewMJwtVerifierWithKeyStore(nil, kStore)
+		_, _, err = ExtractClaims[testClaims](m, token)
+		assert.Error(t, err)
+		assert.ErrorIs(t, err, ErrNoPublicKeyFound)
+	})
+
+	t.Run("TestKIDNonExist", func(t *testing.T) {
+		t.Parallel()
+		kStore.SetKey(mt_ExtraKID, key2)
+		assert.Contains(t, kStore.ListKeys(), mt_ExtraKID)
+
+		s := NewMJwtSignerWithKeyStore("mjwt.test", key, kStore)
+		token, err := s.GenerateJwtWithKID("1", "test", nil, 10*time.Minute, testClaims{TestValue: "test"}, mt_ExtraKID)
+		assert.NoError(t, err)
+
+		kStore.RemoveKey(mt_ExtraKID)
+		assert.NotContains(t, kStore.ListKeys(), mt_ExtraKID)
+
+		m := NewMJwtVerifierWithKeyStore(&key.PublicKey, kStore)
+		_, _, err = ExtractClaims[testClaims](m, token)
+		assert.Error(t, err)
+		assert.ErrorIs(t, err, ErrNoPublicKeyFound)
+	})
 }
diff --git a/signer.go b/signer.go
index 3959619..2679dbd 100644
--- a/signer.go
+++ b/signer.go
@@ -11,6 +11,9 @@ import (
 	"time"
 )
 
+var ErrNoPrivateKeyFound = errors.New("no private key found")
+var ErrSignerNil = errors.New("signer nil")
+
 // defaultMJwtSigner implements Signer and uses an rsa.PrivateKey and issuer name
 // to generate MJWT tokens
 type defaultMJwtSigner struct {
@@ -37,7 +40,7 @@ func NewMJwtSignerWithKeyStore(issuer string, key *rsa.PrivateKey, kStore KeySto
 	return &defaultMJwtSigner{
 		issuer: issuer,
 		key:    key,
-		verify: NewMjwtVerifierWithKeyStore(pKey, kStore).(*defaultMJwtVerifier),
+		verify: NewMJwtVerifierWithKeyStore(pKey, kStore).(*defaultMJwtVerifier),
 	}
 }
 
@@ -101,7 +104,7 @@ func (d *defaultMJwtSigner) Issuer() string {
 // GenerateJwt generates and returns a JWT string using the sub, id, duration and claims; uses the default key
 func (d *defaultMJwtSigner) GenerateJwt(sub, id string, aud jwt.ClaimStrings, dur time.Duration, claims Claims) (string, error) {
 	if d == nil {
-		return "", errors.New("signer nil")
+		return "", ErrSignerNil
 	}
 	return d.SignJwt(wrapClaims[Claims](d, sub, id, aud, dur, claims))
 }
@@ -110,10 +113,10 @@ func (d *defaultMJwtSigner) GenerateJwt(sub, id string, aud jwt.ClaimStrings, du
 // GenerateJwt but is available for signing custom structs; uses the default key
 func (d *defaultMJwtSigner) SignJwt(wrapped jwt.Claims) (string, error) {
 	if d == nil {
-		return "", errors.New("signer nil")
+		return "", ErrSignerNil
 	}
 	if d.key == nil {
-		return "", errors.New("no private key found")
+		return "", ErrNoPrivateKeyFound
 	}
 	token := jwt.NewWithClaims(jwt.SigningMethodRS512, wrapped)
 	return token.SignedString(d.key)
@@ -122,7 +125,7 @@ func (d *defaultMJwtSigner) SignJwt(wrapped jwt.Claims) (string, error) {
 // GenerateJwtWithKID generates and returns a JWT string using the sub, id, duration and claims; this gets signed with the specified kID
 func (d *defaultMJwtSigner) GenerateJwtWithKID(sub, id string, aud jwt.ClaimStrings, dur time.Duration, claims Claims, kID string) (string, error) {
 	if d == nil {
-		return "", errors.New("signer nil")
+		return "", ErrSignerNil
 	}
 	return d.SignJwtWithKID(wrapClaims[Claims](d, sub, id, aud, dur, claims), kID)
 }
@@ -131,11 +134,11 @@ func (d *defaultMJwtSigner) GenerateJwtWithKID(sub, id string, aud jwt.ClaimStri
 // GenerateJwt but is available for signing custom structs; this gets signed with the specified kID
 func (d *defaultMJwtSigner) SignJwtWithKID(wrapped jwt.Claims, kID string) (string, error) {
 	if d == nil {
-		return "", errors.New("signer nil")
+		return "", ErrSignerNil
 	}
 	pKey := d.verify.GetKeyStore().GetKey(kID)
 	if pKey == nil {
-		return "", errors.New("no private key found")
+		return "", ErrNoPrivateKeyFound
 	}
 	token := jwt.NewWithClaims(jwt.SigningMethodRS512, wrapped)
 	token.Header["kid"] = kID
@@ -145,7 +148,7 @@ func (d *defaultMJwtSigner) SignJwtWithKID(wrapped jwt.Claims, kID string) (stri
 // VerifyJwt validates and parses MJWT tokens see defaultMJwtVerifier.VerifyJwt()
 func (d *defaultMJwtSigner) VerifyJwt(token string, claims baseTypeClaim) (*jwt.Token, error) {
 	if d == nil {
-		return nil, errors.New("signer nil")
+		return nil, ErrSignerNil
 	}
 	return d.verify.VerifyJwt(token, claims)
 }
diff --git a/signer_test.go b/signer_test.go
index 468b8e0..f04fbae 100644
--- a/signer_test.go
+++ b/signer_test.go
@@ -16,30 +16,27 @@ import (
 const st_prvExt = "prv"
 const st_pubExt = "pub"
 
-func setupTestDirSigner(t *testing.T, genKeys bool) (string, *rsa.PrivateKey, func(t *testing.T)) {
+func setupTestDirSigner(t *testing.T) (string, *rsa.PrivateKey, func(t *testing.T)) {
 	tempDir, err := os.MkdirTemp("", "this-is-a-test-dir")
 	assert.NoError(t, err)
 
 	var key3 *rsa.PrivateKey = nil
+	key1, err := rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	err = rsaprivate.Write(path.Join(tempDir, "key1.pem."+st_prvExt), key1)
+	assert.NoError(t, err)
 
-	if genKeys {
-		key1, err := rsa.GenerateKey(rand.Reader, 2048)
-		assert.NoError(t, err)
-		err = rsaprivate.Write(path.Join(tempDir, "key1.pem."+st_prvExt), key1)
-		assert.NoError(t, err)
+	key2, err := rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	err = rsaprivate.Write(path.Join(tempDir, "key2.pem."+st_prvExt), key2)
+	assert.NoError(t, err)
+	err = rsapublic.Write(path.Join(tempDir, "key2.pem."+st_pubExt), &key2.PublicKey)
+	assert.NoError(t, err)
 
-		key2, err := rsa.GenerateKey(rand.Reader, 2048)
-		assert.NoError(t, err)
-		err = rsaprivate.Write(path.Join(tempDir, "key2.pem."+st_prvExt), key2)
-		assert.NoError(t, err)
-		err = rsapublic.Write(path.Join(tempDir, "key2.pem."+st_pubExt), &key2.PublicKey)
-		assert.NoError(t, err)
-
-		key3, err = rsa.GenerateKey(rand.Reader, 2048)
-		assert.NoError(t, err)
-		err = rsapublic.Write(path.Join(tempDir, "key3.pem."+st_pubExt), &key3.PublicKey)
-		assert.NoError(t, err)
-	}
+	key3, err = rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	err = rsapublic.Write(path.Join(tempDir, "key3.pem."+st_pubExt), &key3.PublicKey)
+	assert.NoError(t, err)
 
 	return tempDir, key3, func(t *testing.T) {
 		err := os.RemoveAll(tempDir)
@@ -118,7 +115,7 @@ func TestReadOrCreatePrivateKey(t *testing.T) {
 func TestNewMJwtSignerFromDirectory(t *testing.T) {
 	t.Parallel()
 
-	tempDir, prvKey3, cleaner := setupTestDirSigner(t, true)
+	tempDir, prvKey3, cleaner := setupTestDirSigner(t)
 	defer cleaner(t)
 
 	signer, err := NewMJwtSignerFromDirectory("Test", tempDir, st_prvExt, st_pubExt)
@@ -135,7 +132,7 @@ func TestNewMJwtSignerFromDirectory(t *testing.T) {
 func TestNewMJwtSignerFromFileAndDirectory(t *testing.T) {
 	t.Parallel()
 
-	tempDir, prvKey3, cleaner := setupTestDirSigner(t, true)
+	tempDir, prvKey3, cleaner := setupTestDirSigner(t)
 	defer cleaner(t)
 
 	signer, err := NewMJwtSignerFromFileAndDirectory("Test", path.Join(tempDir, "key1.pem."+st_prvExt), tempDir, st_prvExt, st_pubExt)
diff --git a/verifier.go b/verifier.go
index b8abe80..05b8a2b 100644
--- a/verifier.go
+++ b/verifier.go
@@ -7,6 +7,10 @@ import (
 	"github.com/golang-jwt/jwt/v4"
 )
 
+var ErrNoPublicKeyFound = errors.New("no public key found")
+var ErrKIDInvalid = errors.New("kid invalid")
+var ErrVerifierNil = errors.New("verifier nil")
+
 // defaultMJwtVerifier implements Verifier and uses a rsa.PublicKey to validate
 // MJWT tokens
 type defaultMJwtVerifier struct {
@@ -18,12 +22,12 @@ var _ Verifier = &defaultMJwtVerifier{}
 
 // NewMJwtVerifier creates a new defaultMJwtVerifier using the rsa.PublicKey
 func NewMJwtVerifier(key *rsa.PublicKey) Verifier {
-	return NewMjwtVerifierWithKeyStore(key, NewMJwtKeyStore())
+	return NewMJwtVerifierWithKeyStore(key, NewMJwtKeyStore())
 }
 
-// NewMjwtVerifierWithKeyStore creates a new defaultMJwtVerifier using a rsa.PublicKey as the non kID key
+// NewMJwtVerifierWithKeyStore creates a new defaultMJwtVerifier using a rsa.PublicKey as the non kID key
 // and a KeyStore for kID based keys
-func NewMjwtVerifierWithKeyStore(defaultKey *rsa.PublicKey, kStore KeyStore) Verifier {
+func NewMJwtVerifierWithKeyStore(defaultKey *rsa.PublicKey, kStore KeyStore) Verifier {
 	return &defaultMJwtVerifier{pub: defaultKey, kStore: kStore}
 }
 
@@ -62,13 +66,13 @@ func NewMJwtVerifierFromFileAndDirectory(file, directory, prvExt, pubExt string)
 		}
 	}
 
-	return NewMjwtVerifierWithKeyStore(pub, kStore), nil
+	return NewMJwtVerifierWithKeyStore(pub, kStore), nil
 }
 
 // VerifyJwt validates and parses MJWT tokens and returns the claims
 func (d *defaultMJwtVerifier) VerifyJwt(token string, claims baseTypeClaim) (*jwt.Token, error) {
 	if d == nil {
-		return nil, errors.New("verifier nil")
+		return nil, ErrVerifierNil
 	}
 	withClaims, err := jwt.ParseWithClaims(token, claims, func(token *jwt.Token) (interface{}, error) {
 		kIDI, exs := token.Header["kid"]
@@ -77,16 +81,16 @@ func (d *defaultMJwtVerifier) VerifyJwt(token string, claims baseTypeClaim) (*jw
 			if ok {
 				key := d.kStore.GetKeyPublic(kID)
 				if key == nil {
-					return nil, errors.New("no public key found")
+					return nil, ErrNoPublicKeyFound
 				} else {
 					return key, nil
 				}
 			} else {
-				return nil, errors.New("kid invalid")
+				return nil, ErrKIDInvalid
 			}
 		}
 		if d.pub == nil {
-			return nil, errors.New("no public key found")
+			return nil, ErrNoPublicKeyFound
 		}
 		return d.pub, nil
 	})