diff --git a/go.mod b/go.mod
index 6cc49d4..6bb573b 100644
--- a/go.mod
+++ b/go.mod
@@ -14,5 +14,6 @@ require (
 	github.com/opentracing/opentracing-go v1.2.0 // indirect
 	github.com/patrickmn/go-cache v2.1.0+incompatible
 	github.com/sirupsen/logrus v1.8.1
+	github.com/stretchr/testify v1.7.0
 	golang.org/x/crypto v0.0.0-20201216223049-8b5274cf687f
 )
diff --git a/go.sum b/go.sum
index ebf04cd..d87d45f 100644
--- a/go.sum
+++ b/go.sum
@@ -67,6 +67,8 @@ github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXf
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
 github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20201216223049-8b5274cf687f h1:aZp0e2vLN4MToVqnjNEYEtrEA8RH8U8FN1CU7JgqsPU=
@@ -94,3 +96,5 @@ gopkg.in/ini.v1 v1.57.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=
 gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/internal/s3/mock_test.go b/internal/s3/mock_test.go
new file mode 100644
index 0000000..f2747f8
--- /dev/null
+++ b/internal/s3/mock_test.go
@@ -0,0 +1,162 @@
+package s3_test
+
+import (
+	"context"
+	"io/ioutil"
+	"strings"
+	"testing"
+	"time"
+
+	"git.kapelle.org/niklas/s3browser/internal/s3"
+	"git.kapelle.org/niklas/s3browser/internal/types"
+	"github.com/stretchr/testify/assert"
+)
+
+func setup(t *testing.T) (s3.S3Service, context.Context, *assert.Assertions) {
+	service, _ := s3.NewMockS3([]string{"bucket1", "bucket2"})
+	ctx := context.Background()
+	assert := assert.New(t)
+
+	return service, ctx, assert
+}
+
+func TestBuckets(t *testing.T) {
+	s3, ctx, assert := setup(t)
+
+	buckets, err := s3.ListBuckets(ctx)
+	assert.NoError(err)
+
+	assert.Len(buckets, 2)
+
+	assert.Contains(buckets, "bucket1")
+	assert.Contains(buckets, "bucket2")
+}
+
+func TestPut(t *testing.T) {
+	s3, ctx, assert := setup(t)
+	content := "FileContent"
+
+	err := s3.PutObject(ctx, *types.ParseID("bucket1:/file1"), strings.NewReader(content), int64(len(content)))
+	assert.NoError(err)
+}
+
+func TestPutAndGet(t *testing.T) {
+	s3, ctx, assert := setup(t)
+
+	content := "FileContent"
+	id := *types.ParseID("bucket1:/file1")
+
+	err := s3.PutObject(ctx, *types.ParseID("bucket1:/file1"), strings.NewReader(content), int64(len(content)))
+	assert.NoError(err)
+
+	reader, err := s3.GetObject(ctx, id)
+	assert.NoError(err)
+
+	readerContent, err := ioutil.ReadAll(reader)
+	assert.NoError(err)
+
+	assert.Equal(content, string(readerContent))
+}
+
+func TestStat(t *testing.T) {
+	s3, ctx, assert := setup(t)
+
+	content := "FileContent"
+	id := *types.ParseID("bucket1:/file1")
+
+	now := time.Now()
+
+	err := s3.PutObject(ctx, id, strings.NewReader(content), int64(len(content)))
+	assert.NoError(err)
+
+	obj, err := s3.StatObject(ctx, id)
+	assert.NoError(err)
+
+	assert.Equal(id.String(), obj.ID.String())
+	assert.Equal(int64(len(content)), obj.Size)
+	assert.NotEmpty(obj.ETag)
+	assert.WithinDuration(now, obj.LastModified, time.Second*1)
+}
+
+func TestRemove(t *testing.T) {
+	s3, ctx, assert := setup(t)
+
+	content := "FileContent"
+	id := *types.ParseID("bucket1:/file1")
+
+	err := s3.PutObject(ctx, id, strings.NewReader(content), int64(len(content)))
+	assert.NoError(err)
+
+	err = s3.RemoveObject(ctx, id)
+	assert.NoError(err)
+
+	_, err = s3.StatObject(ctx, id)
+	assert.Error(err)
+}
+
+func TestList(t *testing.T) {
+	s3, ctx, assert := setup(t)
+
+	content1 := "FileContent1"
+	id1 := *types.ParseID("bucket1:/file1")
+
+	err := s3.PutObject(ctx, id1, strings.NewReader(content1), int64(len(content1)))
+	assert.NoError(err)
+
+	content2 := "FileContent2"
+	id2 := *types.ParseID("bucket1:/file2")
+
+	err = s3.PutObject(ctx, id2, strings.NewReader(content2), int64(len(content2)))
+	assert.NoError(err)
+
+	listID := types.ParseID("bucket1:/")
+
+	objects, err := s3.ListObjects(ctx, *listID)
+	assert.NoError(err)
+
+	assert.Len(objects, 2)
+}
+
+func TestListRecursive(t *testing.T) {
+	s3, ctx, assert := setup(t)
+
+	s3.PutObject(ctx, *types.ParseID("bucket1:/file1"), strings.NewReader("content"), int64(len("content")))
+	s3.PutObject(ctx, *types.ParseID("bucket1:/path1/file1"), strings.NewReader("content"), int64(len("content")))
+	s3.PutObject(ctx, *types.ParseID("bucket1:/path1/file2"), strings.NewReader("content"), int64(len("content")))
+	s3.PutObject(ctx, *types.ParseID("bucket1:/path1/path2/file1"), strings.NewReader("content"), int64(len("content")))
+	s3.PutObject(ctx, *types.ParseID("bucket1:/path3/path4/file1"), strings.NewReader("content"), int64(len("content")))
+
+	objects, err := s3.ListObjectsRecursive(ctx, *types.ParseID("bucket1:/path1/"))
+	assert.NoError(err)
+	assert.Len(objects, 3)
+}
+
+func TestCopy(t *testing.T) {
+	s3, ctx, assert := setup(t)
+
+	id1 := *types.ParseID("bucket1:/file1")
+	id2 := *types.ParseID("bucket1:/file2")
+
+	s3.PutObject(ctx, id1, strings.NewReader("content"), int64(len("content")))
+
+	err := s3.CopyObject(ctx, id1, id2)
+	assert.NoError(err)
+
+	obj1, err := s3.StatObject(ctx, id1)
+	assert.NoError(err)
+	assert.NotNil(obj1)
+
+	obj2, err := s3.StatObject(ctx, id1)
+	assert.NoError(err)
+	assert.NotNil(obj2)
+
+	assert.Equal(obj1.ETag, obj2.ETag)
+	assert.Equal(obj1.Size, obj2.Size)
+
+	obj2Reader, err := s3.GetObject(ctx, id2)
+	assert.NoError(err)
+
+	obj2Content, err := ioutil.ReadAll(obj2Reader)
+	assert.NoError(err)
+	assert.Equal([]byte("content"), obj2Content)
+}
diff --git a/internal/types/id_test.go b/internal/types/id_test.go
new file mode 100644
index 0000000..0b41b57
--- /dev/null
+++ b/internal/types/id_test.go
@@ -0,0 +1,109 @@
+package types_test
+
+import (
+	"testing"
+
+	"git.kapelle.org/niklas/s3browser/internal/types"
+	"github.com/stretchr/testify/assert"
+)
+
+// TODO: test version component (not yet used in code)
+
+func TestIDParse(t *testing.T) {
+	assert := assert.New(t)
+
+	id := types.ParseID("test:/path/key")
+
+	assert.NotNil(id)
+	assert.True(id.Valid())
+	assert.Equal("test", id.Bucket)
+	assert.Equal("/path/key", id.Key)
+	assert.False(id.IsDirectory())
+	assert.Equal("key", id.Name())
+	assert.Equal("test:/path/key", id.String())
+}
+
+func TestIDParseInvalid(t *testing.T) {
+	assert := assert.New(t)
+
+	assert.Nil(types.ParseID("/asd/ad"))
+	assert.Nil(types.ParseID("test"))
+	assert.Nil(types.ParseID("test:"))
+	assert.Nil(types.ParseID(""))
+	assert.Nil(types.ParseID("/"))
+}
+
+func TestIDIsDir(t *testing.T) {
+	assert := assert.New(t)
+
+	idFile := types.ParseID("test:/path/key")
+	assert.NotNil(idFile)
+	assert.False(idFile.IsDirectory())
+
+	idDir := types.ParseID("test:/path/key/")
+	assert.NotNil(idDir)
+	assert.True(idDir.IsDirectory())
+}
+
+func TestIDRoot(t *testing.T) {
+	assert := assert.New(t)
+
+	id := types.ParseID("test:/")
+
+	assert.NotNil(id)
+	assert.True(id.Valid())
+	assert.Equal("test", id.Bucket)
+	assert.Equal("/", id.Key)
+	assert.True(id.IsDirectory())
+	assert.Equal("/", id.Name())
+	assert.Equal("test:/", id.String())
+
+	assert.Nil(id.Parent())
+}
+
+func TestIDParentFromFile(t *testing.T) {
+	assert := assert.New(t)
+
+	id := types.ParseID("test:/path1/path2/key")
+
+	assert.NotNil(id)
+
+	parent := id.Parent()
+
+	assert.NotNil(parent)
+	assert.True(parent.Valid())
+	assert.Equal("test", parent.Bucket)
+	assert.Equal("/path1/path2/", parent.Key)
+	assert.True(parent.IsDirectory())
+	assert.Equal("path2", parent.Name())
+	assert.Equal("test:/path1/path2/", parent.String())
+}
+
+func TestIDParentFromDir(t *testing.T) {
+	assert := assert.New(t)
+
+	id := types.ParseID("test:/path1/path2/")
+
+	assert.NotNil(id)
+
+	parent := id.Parent()
+
+	assert.NotNil(parent)
+	assert.True(parent.Valid())
+	assert.Equal("test", parent.Bucket)
+	assert.Equal("/path1/", parent.Key)
+	assert.True(parent.IsDirectory())
+	assert.Equal("path1", parent.Name())
+	assert.Equal("test:/path1/", parent.String())
+}
+
+func TestIDParentRoot(t *testing.T) {
+	assert := assert.New(t)
+
+	id := types.ParseID("test:/key1")
+
+	parent := id.Parent()
+
+	assert.NotNil(parent)
+	assert.Equal("/", parent.Key)
+}