diff --git a/internal/build/helper_test.go b/internal/build/helper_test.go
new file mode 100644
index 0000000000..280c547991
--- /dev/null
+++ b/internal/build/helper_test.go
@@ -0,0 +1,173 @@
+package build_test
+
+import (
+	"archive/tar"
+	"bytes"
+	"io"
+	"path/filepath"
+	"testing"
+
+	"github.com/buildpacks/lifecycle/buildpack"
+	"github.com/buildpacks/pack/internal/build"
+	"github.com/buildpacks/pack/pkg/logging"
+	h "github.com/buildpacks/pack/testhelpers"
+	"github.com/heroku/color"
+	"github.com/sclevine/spec"
+	"github.com/sclevine/spec/report"
+)
+
+func TestHelper(t *testing.T) {
+	color.Disable(true)
+	defer color.Disable(false)
+	spec.Run(t, "helperForBuildExtension", testHelper, spec.Report(report.Terminal{}), spec.Sequential())
+}
+
+func testHelper(t *testing.T, when spec.G, it spec.S) {
+	var (
+		tmpDir     string
+		extensions build.Extensions
+		logger     *logging.LogWithWriters
+	)
+	it.Before(func() {
+		var outBuf bytes.Buffer
+		logger = logging.NewLogWithWriters(&outBuf, &outBuf)
+	})
+	when("set-extensions", func() {
+		it("should set single extension", func() {
+			tmpDir = filepath.Join(".", "testdata", "fake-tmp", "build-extension", "single")
+			expectedExtension := build.Extensions{
+				Extensions: []buildpack.GroupElement{
+					{
+						ID:       "samples/test",
+						Version:  "0.0.1",
+						API:      "0.9",
+						Homepage: "https://github.com/buildpacks/samples/test/main/extensions/test",
+					},
+				},
+			}
+			extensions.SetExtensions(tmpDir, logger)
+			h.AssertEq(t, extensions.Extensions[0].ID, expectedExtension.Extensions[0].ID)
+			h.AssertEq(t, extensions.Extensions[0].Version, expectedExtension.Extensions[0].Version)
+			h.AssertEq(t, extensions.Extensions[0].API, expectedExtension.Extensions[0].API)
+			h.AssertEq(t, extensions.Extensions[0].Homepage, expectedExtension.Extensions[0].Homepage)
+		})
+		it("should set multiple extensions", func() {
+			tmpDir = filepath.Join(".", "testdata", "fake-tmp", "build-extension", "multi")
+			expectedExtension := build.Extensions{
+				Extensions: []buildpack.GroupElement{
+					{
+						ID:       "samples/tree",
+						Version:  "0.0.1",
+						API:      "0.9",
+						Homepage: "https://github.com/buildpacks/samples/tree/main/extensions/tree",
+					},
+					{
+						ID:       "samples/test",
+						Version:  "0.0.1",
+						API:      "0.9",
+						Homepage: "https://github.com/buildpacks/samples/test/main/extensions/test",
+					},
+				}}
+			extensions.SetExtensions(tmpDir, logger)
+			h.AssertEq(t, extensions.Extensions[0].ID, expectedExtension.Extensions[0].ID)
+			h.AssertEq(t, extensions.Extensions[0].Version, expectedExtension.Extensions[0].Version)
+			h.AssertEq(t, extensions.Extensions[0].API, expectedExtension.Extensions[0].API)
+			h.AssertEq(t, extensions.Extensions[0].Homepage, expectedExtension.Extensions[0].Homepage)
+			h.AssertEq(t, extensions.Extensions[1].ID, expectedExtension.Extensions[1].ID)
+			h.AssertEq(t, extensions.Extensions[1].Version, expectedExtension.Extensions[1].Version)
+			h.AssertEq(t, extensions.Extensions[1].API, expectedExtension.Extensions[1].API)
+			h.AssertEq(t, extensions.Extensions[1].Homepage, expectedExtension.Extensions[1].Homepage)
+		})
+	})
+
+	when("set dockerfiles", func() {
+		it("should set dockerfiles for single extension", func() {
+			tmpDir = filepath.Join(".", "testdata", "fake-tmp", "build-extension", "single")
+			expectedDockerfile := build.DockerfileInfo{
+				Info: &buildpack.DockerfileInfo{
+					ExtensionID: "samples/test",
+					Kind:        build.DockerfileKindBuild,
+					Path:        filepath.Join(".", "testdata", "fake-tmp", "build-extension", "single", "build", "samples_test", "Dockerfile"),
+				},
+			}
+			extensions.SetExtensions(tmpDir, logger)
+			dockerfiles, err := extensions.DockerFiles(build.DockerfileKindBuild, tmpDir, logger)
+			h.AssertNil(t, err)
+			h.AssertEq(t, dockerfiles[0].Info.ExtensionID, expectedDockerfile.Info.ExtensionID)
+			h.AssertEq(t, dockerfiles[0].Info.Kind, expectedDockerfile.Info.Kind)
+			h.AssertEq(t, dockerfiles[0].Info.Path, expectedDockerfile.Info.Path)
+		})
+		it("should set dockerfiles for multiple extensions", func() {
+			tmpDir = filepath.Join(".", "testdata", "fake-tmp", "build-extension", "multi")
+			expectedDockerfiles := []build.DockerfileInfo{
+				{
+					Info: &buildpack.DockerfileInfo{
+						ExtensionID: "samples/tree",
+						Kind:        build.DockerfileKindBuild,
+						Path:        filepath.Join(".", "testdata", "fake-tmp", "build-extension", "multi", "build", "samples_tree", "Dockerfile"),
+					},
+				},
+				{
+					Info: &buildpack.DockerfileInfo{
+						ExtensionID: "samples/test",
+						Kind:        build.DockerfileKindBuild,
+						Path:        filepath.Join(".", "testdata", "fake-tmp", "build-extension", "multi", "build", "samples_test", "Dockerfile"),
+					},
+				},
+			}
+			extensions.SetExtensions(tmpDir, logger)
+			dockerfiles, err := extensions.DockerFiles(build.DockerfileKindBuild, tmpDir, logger)
+			h.AssertNil(t, err)
+			h.AssertEq(t, dockerfiles[0].Info.ExtensionID, expectedDockerfiles[0].Info.ExtensionID)
+			h.AssertEq(t, dockerfiles[0].Info.Kind, expectedDockerfiles[0].Info.Kind)
+			h.AssertEq(t, dockerfiles[0].Info.Path, expectedDockerfiles[0].Info.Path)
+			h.AssertEq(t, dockerfiles[1].Info.ExtensionID, expectedDockerfiles[1].Info.ExtensionID)
+			h.AssertEq(t, dockerfiles[1].Info.Kind, expectedDockerfiles[1].Info.Kind)
+			h.AssertEq(t, dockerfiles[1].Info.Path, expectedDockerfiles[1].Info.Path)
+		})
+	})
+
+	when("create build context", func() {
+		it("should create build context", func() {
+			tmpDir = filepath.Join(".", "testdata", "fake-tmp", "build-extension", "single")
+			extensions.SetExtensions(tmpDir, logger)
+			dockerfiles, err := extensions.DockerFiles(build.DockerfileKindBuild, tmpDir, logger)
+			h.AssertNil(t, err)
+			buildContext, err := dockerfiles[0].CreateBuildContext(tmpDir)
+			h.AssertNil(t, err)
+			tr := tar.NewReader(buildContext)
+			checkDirectoryInTar(t, tr, "/workspace/build")
+			checkFileInTar(t, tr, "Dockerfile")
+		})
+	})
+}
+
+func checkDirectoryInTar(t *testing.T, tr *tar.Reader, directoryName string) {
+	for {
+		header, err := tr.Next()
+		if err == io.EOF {
+			t.Fatalf("directory %s not found", directoryName)
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		if header.Name == directoryName && header.Typeflag == tar.TypeDir {
+			return
+		}
+	}
+}
+
+func checkFileInTar(t *testing.T, tr *tar.Reader, fileName string) {
+	for {
+		header, err := tr.Next()
+		if err == io.EOF {
+			t.Fatalf("file %s not found", fileName)
+		}
+		if err != nil {
+			t.Fatal(err)
+		}
+		if header.Name == fileName && header.Typeflag == tar.TypeReg {
+			return
+		}
+	}
+}