diff --git a/internal/homesick/core/generate_test.go b/internal/homesick/core/generate_test.go
new file mode 100644
index 0000000..76b4ad6
--- /dev/null
+++ b/internal/homesick/core/generate_test.go
@@ -0,0 +1,69 @@
+package core_test
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"git.hrafn.xyz/aether/gosick/internal/homesick/core"
+	"github.com/stretchr/testify/require"
+	"github.com/stretchr/testify/suite"
+)
+
+type GenerateSuite struct {
+	suite.Suite
+	tmpDir string
+	app    *core.App
+}
+
+func TestGenerateSuite(t *testing.T) {
+	suite.Run(t, new(GenerateSuite))
+}
+
+func (s *GenerateSuite) SetupTest() {
+	s.tmpDir = s.T().TempDir()
+	s.app = &core.App{
+		HomeDir:  filepath.Join(s.tmpDir, "home"),
+		ReposDir: filepath.Join(s.tmpDir, "home", ".homesick", "repos"),
+		Stdout:   io.Discard,
+		Stderr:   io.Discard,
+	}
+}
+
+func (s *GenerateSuite) TestGenerate_CreatesGitRepoAndHomeDir() {
+	castlePath := filepath.Join(s.tmpDir, "my-castle")
+
+	require.NoError(s.T(), s.app.Generate(castlePath))
+	require.DirExists(s.T(), castlePath)
+	require.DirExists(s.T(), filepath.Join(castlePath, ".git"))
+	require.DirExists(s.T(), filepath.Join(castlePath, "home"))
+}
+
+func (s *GenerateSuite) TestGenerate_AddsOriginWhenGitHubUserConfigured() {
+	castlePath := filepath.Join(s.tmpDir, "my-castle")
+	gitConfig := filepath.Join(s.tmpDir, "gitconfig")
+	require.NoError(s.T(), os.WriteFile(gitConfig, []byte("[github]\n\tuser = octocat\n"), 0o644))
+	s.T().Setenv("GIT_CONFIG_GLOBAL", gitConfig)
+	s.T().Setenv("GIT_CONFIG_NOSYSTEM", "1")
+
+	require.NoError(s.T(), s.app.Generate(castlePath))
+
+	configPath := filepath.Join(castlePath, ".git", "config")
+	content, err := os.ReadFile(configPath)
+	require.NoError(s.T(), err)
+	require.Contains(s.T(), string(content), "git@github.com:octocat/my-castle.git")
+}
+
+func (s *GenerateSuite) TestGenerate_DoesNotAddOriginWhenGitHubUserMissing() {
+	castlePath := filepath.Join(s.tmpDir, "my-castle")
+	s.T().Setenv("GIT_CONFIG_GLOBAL", filepath.Join(s.tmpDir, "nonexistent-config"))
+	s.T().Setenv("GIT_CONFIG_NOSYSTEM", "1")
+
+	require.NoError(s.T(), s.app.Generate(castlePath))
+
+	configPath := filepath.Join(castlePath, ".git", "config")
+	content, err := os.ReadFile(configPath)
+	require.NoError(s.T(), err)
+	require.NotContains(s.T(), string(content), "[remote \"origin\"]")
+}
diff --git a/internal/homesick/core/open_test.go b/internal/homesick/core/open_test.go
new file mode 100644
index 0000000..16eefb2
--- /dev/null
+++ b/internal/homesick/core/open_test.go
@@ -0,0 +1,86 @@
+package core_test
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"git.hrafn.xyz/aether/gosick/internal/homesick/core"
+	git "github.com/go-git/go-git/v5"
+	"github.com/stretchr/testify/require"
+	"github.com/stretchr/testify/suite"
+)
+
+type OpenSuite struct {
+	suite.Suite
+	tmpDir   string
+	homeDir  string
+	reposDir string
+	stdout   *bytes.Buffer
+	stderr   *bytes.Buffer
+	app      *core.App
+}
+
+func TestOpenSuite(t *testing.T) {
+	suite.Run(t, new(OpenSuite))
+}
+
+func (s *OpenSuite) SetupTest() {
+	s.tmpDir = s.T().TempDir()
+	s.homeDir = filepath.Join(s.tmpDir, "home")
+	s.reposDir = filepath.Join(s.homeDir, ".homesick", "repos")
+	require.NoError(s.T(), os.MkdirAll(s.reposDir, 0o755))
+
+	s.stdout = &bytes.Buffer{}
+	s.stderr = &bytes.Buffer{}
+	s.app = &core.App{
+		HomeDir:  s.homeDir,
+		ReposDir: s.reposDir,
+		Stdout:   s.stdout,
+		Stderr:   s.stderr,
+	}
+}
+
+func (s *OpenSuite) createCastleRepo(castle string) string {
+	castleRoot := filepath.Join(s.reposDir, castle)
+	require.NoError(s.T(), os.MkdirAll(filepath.Join(castleRoot, "home"), 0o755))
+	_, err := git.PlainInit(castleRoot, false)
+	require.NoError(s.T(), err)
+	return castleRoot
+}
+
+func (s *OpenSuite) TestOpen_RequiresEditorEnv() {
+	s.createCastleRepo("dotfiles")
+	s.T().Setenv("EDITOR", "")
+
+	err := s.app.Open("dotfiles")
+	require.Error(s.T(), err)
+	require.Contains(s.T(), err.Error(), "$EDITOR")
+}
+
+func (s *OpenSuite) TestOpen_MissingCastleReturnsError() {
+	s.T().Setenv("EDITOR", "vim")
+
+	err := s.app.Open("missing")
+	require.Error(s.T(), err)
+	require.Contains(s.T(), err.Error(), "could not open")
+}
+
+func (s *OpenSuite) TestOpen_RunsEditorInCastleRoot() {
+	castleRoot := s.createCastleRepo("dotfiles")
+
+	capture := filepath.Join(s.tmpDir, "open_capture.txt")
+	editorScript := filepath.Join(s.tmpDir, "editor.sh")
+	require.NoError(s.T(), os.WriteFile(editorScript, []byte("#!/bin/sh\npwd > \""+capture+"\"\necho \"$1\" >> \""+capture+"\"\n"), 0o755))
+	s.T().Setenv("EDITOR", editorScript)
+
+	require.NoError(s.T(), s.app.Open("dotfiles"))
+
+	content, err := os.ReadFile(capture)
+	require.NoError(s.T(), err)
+	require.Equal(s.T(), castleRoot+"\n.\n", string(content))
+}
+
+var _ io.Writer