add unit tests

Author: mdimiceli

terraform/binary_path.go

@@ -48,13 +48,15 @@ func NewBinary(terraformBinary string) *Binary {
 
 func (binary *Binary) BinaryPath() (string, error) {
 	// if user sets a terraform binary use it
-	exists, err := binary.FS.Exists(binary.TerraformBinary)
-	if err == nil && exists {
-		return binary.TerraformBinary, nil
+	if binary.TerraformBinary != "" {
+		exists, err := binary.FS.Exists(binary.TerraformBinary)
+		if err == nil && exists {
+			return binary.TerraformBinary, nil
+		}
 	}
 
 	destinationPath := fmt.Sprintf("%s/%s", binary.FS.GetTempDir(os.TempDir()), bblTfBinaryName)
-	exists, err = binary.FS.Exists(destinationPath)
+	exists, err := binary.FS.Exists(destinationPath)
 	if err != nil {
 		return "", err
 	}

terraform/binary_path_test.go

@@ -60,6 +60,33 @@ var _ = Describe("BinaryPath", func() {
 		Expect(fileSystem.ChtimesCall.Receives.ModTime).To(Equal(modTime))
 	})
 
+	Context("when a custom terraform binary path is set", func() {
+		BeforeEach(func() {
+			binary.TerraformBinary = "/some/custom/path/bbl-terraform"
+		})
+
+		Context("and the file exists", func() {
+			BeforeEach(func() {
+				fileSystem.ExistsCall.Returns.Bool = true
+			})
+
+			It("doesn't rewrite the file", func() {
+				res, err := binary.BinaryPath()
+				Expect(err).NotTo(HaveOccurred())
+				Expect(res).To(Equal("/some/custom/path/bbl-terraform"))
+				Expect(fileSystem.WriteFileCall.CallCount).To(Equal(0))
+			})
+		})
+
+		Context("but the file does not exist", func() {
+			It("uses the embedded binary ", func() {
+				res, err := binary.BinaryPath()
+				Expect(err).NotTo(HaveOccurred())
+				Expect(res).To(Equal("/some/tmp/path/bbl-terraform"))
+			})
+		})
+	})
+
 	Context("when there is no my-terraform-binary in box", func() {
 		BeforeEach(func() {
 			binary.EmbedData = contentOnlyModTime