diff --git a/go.mod b/go.mod
index 54784f1..181cdd4 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,13 @@ module github.com/romdo/gomockctx
 
 go 1.17
 
-require github.com/golang/mock v1.6.0
+require (
+	github.com/golang/mock v1.6.0
+	github.com/stretchr/testify v1.7.0
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
+)
diff --git a/go.sum b/go.sum
index d067127..50a3a75 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,13 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/golang/mock v1.6.0 h1:ErTB+efbowRARo13NNdxyJji2egdxLGQhRaY+DUumQc=
 github.com/golang/mock v1.6.0/go.mod h1:p6yTPP+5HYm5mzsMV8JkE6ZKdX+/wYM6Hr+LicevLPs=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/yuin/goldmark v1.3.5/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
@@ -23,3 +31,8 @@ golang.org/x/tools v0.1.1/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/gomockctx.go b/gomockctx.go
index d12099d..a8a63e2 100644
--- a/gomockctx.go
+++ b/gomockctx.go
@@ -17,25 +17,6 @@ type (
 
 var ctxKey contextKey = "gomockctx context ID"
 
-func newCtxID() contextValue {
-	id, err := randString(64)
-	if err != nil {
-		panic(err)
-	}
-
-	return contextValue(id)
-}
-
-func value(ctx context.Context) contextValue {
-	var value contextValue
-	v := ctx.Value(ctxKey)
-	if s, ok := v.(contextValue); ok {
-		value = s
-	}
-
-	return value
-}
-
 // New returns a context as a child of the given parent, and with a randomized
 // gomockctx ID value set, making it a gomockctx context. This can then be used
 // with Is to get a gomock Matcher which returns true for the context from New,
@@ -57,8 +38,25 @@ func Is(ctx context.Context) gomock.Matcher {
 	return WithValue(ctxKey, value(ctx))
 }
 
-// WithValue creates a generic gomock context matcher which returns true for any
-// context which has the specified key/value.
+// ID returns the gomockctx ID value in the given context, or a empty string if
+// the context does not have a gomockctx ID value.
+func ID(ctx context.Context) string {
+	if ctx == nil {
+		return ""
+	}
+
+	return string(value(ctx))
+}
+
+// Any returns a gomock.Matcher which matches any context.Context object.
+func Any() gomock.Matcher {
+	return gomock.AssignableToTypeOf(
+		reflect.TypeOf((*context.Context)(nil)).Elem(),
+	)
+}
+
+// WithValue returns a gomock.Matcher which matches any context that has the
+// specified key and value.
 func WithValue(key interface{}, value interface{}) gomock.Matcher {
 	return &contextMatcher{
 		key:   key,
@@ -66,12 +64,6 @@ func WithValue(key interface{}, value interface{}) gomock.Matcher {
 	}
 }
 
-// ID returns the gomockctx ID value in the given context, or a empty string if
-// it not a gomockctx context.
-func ID(ctx context.Context) string {
-	return string(value(ctx))
-}
-
 type contextMatcher struct {
 	key   interface{}
 	value interface{}
@@ -79,15 +71,37 @@ type contextMatcher struct {
 
 var _ gomock.Matcher = &contextMatcher{}
 
-func (e *contextMatcher) Matches(x interface{}) bool {
-	ctx, ok := x.(context.Context)
-	if !ok {
-		return false
+func (cm *contextMatcher) Matches(x interface{}) bool {
+	if ctx, ok := x.(context.Context); ok {
+		return reflect.DeepEqual(cm.value, ctx.Value(cm.key))
 	}
 
-	return reflect.DeepEqual(e.value, ctx.Value(e.key))
+	return false
 }
 
-func (e *contextMatcher) String() string {
-	return fmt.Sprintf(`context with "%+v" = "%+v"`, e.key, e.value)
+func (cm *contextMatcher) String() string {
+	return fmt.Sprintf(`context with "%+v" = "%+v"`, cm.key, cm.value)
+}
+
+func newCtxID() contextValue {
+	id, err := randString(64)
+	if err != nil {
+		panic(err)
+	}
+
+	return contextValue(id)
+}
+
+func value(ctx context.Context) contextValue {
+	var value contextValue
+	if ctx == nil {
+		return value
+	}
+
+	v := ctx.Value(ctxKey)
+	if s, ok := v.(contextValue); ok {
+		value = s
+	}
+
+	return value
 }
diff --git a/gomockctx_test.go b/gomockctx_test.go
new file mode 100644
index 0000000..4f603d0
--- /dev/null
+++ b/gomockctx_test.go
@@ -0,0 +1,41 @@
+package gomockctx
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestID(t *testing.T) {
+	tests := []struct {
+		name string
+		ctx  context.Context
+		want string
+	}{
+		{
+			name: "nil",
+			ctx:  nil,
+			want: "",
+		},
+		{
+			name: "without ID",
+			ctx:  context.Background(),
+			want: "",
+		},
+		{
+			name: "with ID",
+			ctx: context.WithValue(
+				context.Background(), ctxKey, contextValue("xI2UWC8MvdYcU22B"),
+			),
+			want: "xI2UWC8MvdYcU22B",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ID(tt.ctx)
+
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}