diff --git a/solver/boltdbcachestorage/storage_test.go b/solver/boltdbcachestorage/storage_test.go
index a76c7726..69a34999 100644
--- a/solver/boltdbcachestorage/storage_test.go
+++ b/solver/boltdbcachestorage/storage_test.go
@@ -7,11 +7,12 @@ import (
 	"testing"
 
 	"github.com/moby/buildkit/solver"
+	"github.com/moby/buildkit/solver/testutil"
 	"github.com/stretchr/testify/require"
 )
 
 func TestBoltCacheStorage(t *testing.T) {
-	solver.RunCacheStorageTests(t, func() (solver.CacheKeyStorage, func()) {
+	testutil.RunCacheStorageTests(t, func() (solver.CacheKeyStorage, func()) {
 		tmpDir, err := ioutil.TempDir("", "storage")
 		require.NoError(t, err)
 
diff --git a/solver/memorycachestorage_test.go b/solver/memorycachestorage_test.go
deleted file mode 100644
index 69a112ad..00000000
--- a/solver/memorycachestorage_test.go
+++ /dev/null
@@ -1,9 +0,0 @@
-package solver
-
-import "testing"
-
-func TestMemoryCacheStorage(t *testing.T) {
-	RunCacheStorageTests(t, func() (CacheKeyStorage, func()) {
-		return NewInMemoryCacheStorage(), func() {}
-	})
-}
diff --git a/solver/cachestorage_testsuite.go b/solver/testutil/cachestorage_testsuite.go
similarity index 71%
rename from solver/cachestorage_testsuite.go
rename to solver/testutil/cachestorage_testsuite.go
index 1292c553..7bc16aae 100644
--- a/solver/cachestorage_testsuite.go
+++ b/solver/testutil/cachestorage_testsuite.go
@@ -1,19 +1,21 @@
-package solver
+package testutil
 
 import (
+	"fmt"
 	"reflect"
 	"runtime"
 	"strings"
 	"testing"
 	"time"
 
+	"github.com/moby/buildkit/solver"
 	digest "github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/require"
 )
 
-func RunCacheStorageTests(t *testing.T, st func() (CacheKeyStorage, func())) {
-	for _, tc := range []func(*testing.T, CacheKeyStorage){
+func RunCacheStorageTests(t *testing.T, st func() (solver.CacheKeyStorage, func())) {
+	for _, tc := range []func(*testing.T, solver.CacheKeyStorage){
 		testResults,
 		testLinks,
 		testResultReleaseSingleLevel,
@@ -25,7 +27,7 @@ func RunCacheStorageTests(t *testing.T, st func() (CacheKeyStorage, func())) {
 	}
 }
 
-func runStorageTest(t *testing.T, fn func(t *testing.T, st CacheKeyStorage), st func() (CacheKeyStorage, func())) {
+func runStorageTest(t *testing.T, fn func(t *testing.T, st solver.CacheKeyStorage), st func() (solver.CacheKeyStorage, func())) {
 	require.True(t, t.Run(getFunctionName(fn), func(t *testing.T) {
 		s, cleanup := st()
 		defer cleanup()
@@ -33,28 +35,28 @@ func runStorageTest(t *testing.T, fn func(t *testing.T, st CacheKeyStorage), st
 	}))
 }
 
-func testResults(t *testing.T, st CacheKeyStorage) {
+func testResults(t *testing.T, st solver.CacheKeyStorage) {
 	t.Parallel()
-	err := st.AddResult("foo", CacheResult{
+	err := st.AddResult("foo", solver.CacheResult{
 		ID:        "foo0",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	err = st.AddResult("foo", CacheResult{
+	err = st.AddResult("foo", solver.CacheResult{
 		ID:        "foo1",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	err = st.AddResult("bar", CacheResult{
+	err = st.AddResult("bar", solver.CacheResult{
 		ID:        "bar0",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	m := map[string]CacheResult{}
-	err = st.WalkResults("foo", func(r CacheResult) error {
+	m := map[string]solver.CacheResult{}
+	err = st.WalkResults("foo", func(r solver.CacheResult) error {
 		m[r.ID] = r
 		return nil
 	})
@@ -67,8 +69,8 @@ func testResults(t *testing.T, st CacheKeyStorage) {
 	require.True(t, ok)
 	require.True(t, f0.CreatedAt.Before(f1.CreatedAt))
 
-	m = map[string]CacheResult{}
-	err = st.WalkResults("bar", func(r CacheResult) error {
+	m = map[string]solver.CacheResult{}
+	err = st.WalkResults("bar", func(r solver.CacheResult) error {
 		m[r.ID] = r
 		return nil
 	})
@@ -79,7 +81,7 @@ func testResults(t *testing.T, st CacheKeyStorage) {
 	require.True(t, ok)
 
 	// empty result
-	err = st.WalkResults("baz", func(r CacheResult) error {
+	err = st.WalkResults("baz", func(r solver.CacheResult) error {
 		require.Fail(t, "unreachable")
 		return nil
 	})
@@ -92,17 +94,17 @@ func testResults(t *testing.T, st CacheKeyStorage) {
 
 	_, err = st.Load("foo1", "foo1")
 	require.Error(t, err)
-	require.Equal(t, errors.Cause(err), ErrNotFound)
+	require.Equal(t, errors.Cause(err), solver.ErrNotFound)
 
 	_, err = st.Load("foo", "foo2")
 	require.Error(t, err)
-	require.Equal(t, errors.Cause(err), ErrNotFound)
+	require.Equal(t, errors.Cause(err), solver.ErrNotFound)
 }
 
-func testLinks(t *testing.T, st CacheKeyStorage) {
+func testLinks(t *testing.T, st solver.CacheKeyStorage) {
 	t.Parallel()
 
-	l0 := CacheInfoLink{
+	l0 := solver.CacheInfoLink{
 		Input: 0, Output: 1, Digest: digest.FromBytes([]byte(">target0")),
 	}
 	err := st.AddLink("foo", l0, "target0")
@@ -122,7 +124,7 @@ func testLinks(t *testing.T, st CacheKeyStorage) {
 	_, ok := m["target0"]
 	require.True(t, ok)
 
-	l1 := CacheInfoLink{
+	l1 := solver.CacheInfoLink{
 		Input: 0, Output: 1, Digest: digest.FromBytes([]byte(">target1")),
 	}
 	m = map[string]struct{}{}
@@ -163,16 +165,16 @@ func testLinks(t *testing.T, st CacheKeyStorage) {
 	require.True(t, ok)
 }
 
-func testResultReleaseSingleLevel(t *testing.T, st CacheKeyStorage) {
+func testResultReleaseSingleLevel(t *testing.T, st solver.CacheKeyStorage) {
 	t.Parallel()
 
-	err := st.AddResult("foo", CacheResult{
+	err := st.AddResult("foo", solver.CacheResult{
 		ID:        "foo0",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	err = st.AddResult("foo", CacheResult{
+	err = st.AddResult("foo", solver.CacheResult{
 		ID:        "foo1",
 		CreatedAt: time.Now(),
 	})
@@ -182,7 +184,7 @@ func testResultReleaseSingleLevel(t *testing.T, st CacheKeyStorage) {
 	require.NoError(t, err)
 
 	m := map[string]struct{}{}
-	st.WalkResults("foo", func(res CacheResult) error {
+	st.WalkResults("foo", func(res solver.CacheResult) error {
 		m[res.ID] = struct{}{}
 		return nil
 	})
@@ -195,7 +197,7 @@ func testResultReleaseSingleLevel(t *testing.T, st CacheKeyStorage) {
 	require.NoError(t, err)
 
 	m = map[string]struct{}{}
-	st.WalkResults("foo", func(res CacheResult) error {
+	st.WalkResults("foo", func(res solver.CacheResult) error {
 		m[res.ID] = struct{}{}
 		return nil
 	})
@@ -203,31 +205,31 @@ func testResultReleaseSingleLevel(t *testing.T, st CacheKeyStorage) {
 	require.Equal(t, len(m), 0)
 }
 
-func testBacklinks(t *testing.T, st CacheKeyStorage) {
+func testBacklinks(t *testing.T, st solver.CacheKeyStorage) {
 	t.Parallel()
 
-	err := st.AddResult("foo", CacheResult{
+	err := st.AddResult("foo", solver.CacheResult{
 		ID:        "foo-result",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	err = st.AddResult("sub0", CacheResult{
+	err = st.AddResult("sub0", solver.CacheResult{
 		ID:        "sub0-result",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	l0 := CacheInfoLink{
+	l0 := solver.CacheInfoLink{
 		Input: 0, Output: 1, Digest: digest.FromBytes([]byte("to-sub0")),
 	}
 	err = st.AddLink("foo", l0, "sub0")
 	require.NoError(t, err)
 
 	backlinks := 0
-	st.WalkBacklinks("sub0", func(id string, link CacheInfoLink) error {
+	st.WalkBacklinks("sub0", func(id string, link solver.CacheInfoLink) error {
 		require.Equal(t, id, "foo")
-		require.Equal(t, link.Input, Index(0))
+		require.Equal(t, link.Input, solver.Index(0))
 		require.Equal(t, link.Digest, rootKey(digest.FromBytes([]byte("to-sub0")), 1))
 		backlinks++
 		return nil
@@ -235,28 +237,28 @@ func testBacklinks(t *testing.T, st CacheKeyStorage) {
 	require.Equal(t, backlinks, 1)
 }
 
-func testResultReleaseMultiLevel(t *testing.T, st CacheKeyStorage) {
+func testResultReleaseMultiLevel(t *testing.T, st solver.CacheKeyStorage) {
 	t.Parallel()
 
-	err := st.AddResult("foo", CacheResult{
+	err := st.AddResult("foo", solver.CacheResult{
 		ID:        "foo-result",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	err = st.AddResult("sub0", CacheResult{
+	err = st.AddResult("sub0", solver.CacheResult{
 		ID:        "sub0-result",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	l0 := CacheInfoLink{
+	l0 := solver.CacheInfoLink{
 		Input: 0, Output: 1, Digest: digest.FromBytes([]byte("to-sub0")),
 	}
 	err = st.AddLink("foo", l0, "sub0")
 	require.NoError(t, err)
 
-	err = st.AddResult("sub1", CacheResult{
+	err = st.AddResult("sub1", solver.CacheResult{
 		ID:        "sub1-result",
 		CreatedAt: time.Now(),
 	})
@@ -271,7 +273,7 @@ func testResultReleaseMultiLevel(t *testing.T, st CacheKeyStorage) {
 	require.NoError(t, err)
 
 	m := map[string]struct{}{}
-	err = st.WalkResults("foo", func(res CacheResult) error {
+	err = st.WalkResults("foo", func(res solver.CacheResult) error {
 		m[res.ID] = struct{}{}
 		return nil
 	})
@@ -302,7 +304,7 @@ func testResultReleaseMultiLevel(t *testing.T, st CacheKeyStorage) {
 	require.True(t, st.Exists("foo"))
 
 	m = map[string]struct{}{}
-	err = st.WalkResults("foo", func(res CacheResult) error {
+	err = st.WalkResults("foo", func(res solver.CacheResult) error {
 		m[res.ID] = struct{}{}
 		return nil
 	})
@@ -327,22 +329,22 @@ func testResultReleaseMultiLevel(t *testing.T, st CacheKeyStorage) {
 	require.False(t, st.Exists("foo"))
 }
 
-func testWalkIDsByResult(t *testing.T, st CacheKeyStorage) {
+func testWalkIDsByResult(t *testing.T, st solver.CacheKeyStorage) {
 	t.Parallel()
 
-	err := st.AddResult("foo", CacheResult{
+	err := st.AddResult("foo", solver.CacheResult{
 		ID:        "foo-result",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	err = st.AddResult("foo2", CacheResult{
+	err = st.AddResult("foo2", solver.CacheResult{
 		ID:        "foo-result",
 		CreatedAt: time.Now(),
 	})
 	require.NoError(t, err)
 
-	err = st.AddResult("bar", CacheResult{
+	err = st.AddResult("bar", solver.CacheResult{
 		ID:        "bar-result",
 		CreatedAt: time.Now(),
 	})
@@ -370,3 +372,7 @@ func getFunctionName(i interface{}) string {
 	dot := strings.LastIndex(fullname, ".") + 1
 	return strings.Title(fullname[dot:])
 }
+
+func rootKey(dgst digest.Digest, output solver.Index) digest.Digest {
+	return digest.FromBytes([]byte(fmt.Sprintf("%s@%d", dgst, output)))
+}
diff --git a/solver/testutil/memorycachestorage_test.go b/solver/testutil/memorycachestorage_test.go
new file mode 100644
index 00000000..ea1f6be4
--- /dev/null
+++ b/solver/testutil/memorycachestorage_test.go
@@ -0,0 +1,13 @@
+package testutil
+
+import (
+	"testing"
+
+	"github.com/moby/buildkit/solver"
+)
+
+func TestMemoryCacheStorage(t *testing.T) {
+	RunCacheStorageTests(t, func() (solver.CacheKeyStorage, func()) {
+		return solver.NewInMemoryCacheStorage(), func() {}
+	})
+}