File Settings should return error in case the file itself does not exist

infrastructure/file_settings_source.go

@@ -35,6 +35,9 @@ func NewFileSettingsSource(
 }
 
 func (s *FileSettingsSource) PublicSSHKeyForUsername(string) (string, error) {
+	if !s.fs.FileExists(s.settingsFilePath) {
+		return "", bosherr.Error("File for settings source does not exist")
+	}
 	return "", nil
 }
 

infrastructure/file_settings_source_test.go

@@ -26,10 +26,31 @@ var _ = Describe("FileSettingsSource", func() {
 	})
 
 	Describe("PublicSSHKeyForUsername", func() {
-		It("returns an empty string", func() {
-			publicKey, err := source.PublicSSHKeyForUsername("fake-username")
-			Expect(err).ToNot(HaveOccurred())
-			Expect(publicKey).To(Equal(""))
+		Context("when the settings file exists", func() {
+			BeforeEach(func() {
+				settingsFileName := "/fake-settings-file-path"
+				source = infrastructure.NewFileSettingsSource(settingsFileName, fs, logger)
+				err := fs.WriteFileString(settingsFileName, "{}")
+				Expect(err).NotTo(HaveOccurred())
+			})
+
+			It("returns an empty string", func() {
+				publicKey, err := source.PublicSSHKeyForUsername("fake-username")
+				Expect(err).ToNot(HaveOccurred())
+				Expect(publicKey).To(Equal(""))
+			})
+		})
+
+		Context("when the settings file does not exist", func() {
+			BeforeEach(func() {
+				source = infrastructure.NewFileSettingsSource("/missing-settings-file-path", fs, logger)
+			})
+
+			It("returns an error", func() {
+				_, err := source.PublicSSHKeyForUsername("fake-username")
+				Expect(err).To(HaveOccurred())
+				Expect(err.Error()).To(ContainSubstring("File for settings source does not exist"))
+			})
 		})
 	})