feat(cli): add update subcommand for in-place self-update

internal/cli/update_test.go

@@ -0,0 +1,39 @@
+package cli
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestUpdateDryRunPrintsCommand(t *testing.T) {
+	cmd := NewUpdate()
+	var buf bytes.Buffer
+	cmd.SetOut(&buf)
+	cmd.SetErr(&buf)
+	cmd.SetArgs([]string{"--dry-run", "--install-dir", "/tmp/test-dir"})
+	require.NoError(t, cmd.Execute())
+
+	out := buf.String()
+	assert.Contains(t, out, "Installing latest harness-sync into /tmp/test-dir")
+	assert.Contains(t, out, "curl -fsSL")
+	assert.Contains(t, out, "install.sh")
+	assert.Contains(t, out, "INSTALL_DIR=")
+	// Should NOT have run anything
+	assert.False(t, strings.Contains(out, "[INFO]"), "dry run must not invoke install.sh")
+}
+
+func TestUpdateResolvesCurrentBinaryDirByDefault(t *testing.T) {
+	cmd := NewUpdate()
+	var buf bytes.Buffer
+	cmd.SetOut(&buf)
+	cmd.SetArgs([]string{"--dry-run"})
+	require.NoError(t, cmd.Execute())
+
+	// Should mention SOME absolute path (the test binary's directory)
+	out := buf.String()
+	assert.Contains(t, out, "Installing latest harness-sync into /")
+}