diff --git a/internal/handlers/conflicts_test.go b/internal/handlers/conflicts_test.go
new file mode 100644
index 0000000..2c0b97c
--- /dev/null
+++ b/internal/handlers/conflicts_test.go
@@ -0,0 +1,309 @@
+package handlers
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetMostRecentSource_KOReaderMoreRecent(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source:    "koreader",
+			Timestamp: time.Date(2026, 1, 30, 20, 10, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.45,
+				"epubcfi":    "epubcfi(/6/4/2:15)",
+			},
+		},
+		"kobo": {
+			Source:    "kobo",
+			Timestamp: time.Date(2026, 1, 30, 20, 5, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.42,
+				"page":       float64(89),
+			},
+		},
+	}
+
+	source, data := handler.getMostRecentSource(conflictData)
+	assert.Equal(t, "koreader", source)
+	assert.Equal(t, 0.45, data["percentage"])
+}
+
+func TestGetMostRecentSource_KoboMoreRecent(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source:    "koreader",
+			Timestamp: time.Date(2026, 1, 30, 20, 5, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.45,
+			},
+		},
+		"kobo": {
+			Source:    "kobo",
+			Timestamp: time.Date(2026, 1, 30, 20, 15, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.42,
+			},
+		},
+	}
+
+	source, data := handler.getMostRecentSource(conflictData)
+	assert.Equal(t, "kobo", source)
+	assert.Equal(t, 0.42, data["percentage"])
+}
+
+func TestGetMostRecentSource_SingleSource(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source:    "koreader",
+			Timestamp: time.Date(2026, 1, 30, 20, 10, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.50,
+			},
+		},
+	}
+
+	source, data := handler.getMostRecentSource(conflictData)
+	assert.Equal(t, "koreader", source)
+	assert.Equal(t, 0.50, data["percentage"])
+}
+
+func TestGetMostRecentSource_SameTimestamp(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	ts := time.Date(2026, 1, 30, 20, 10, 0, 0, time.UTC)
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source:    "koreader",
+			Timestamp: ts,
+			Data: map[string]interface{}{
+				"percentage": 0.45,
+			},
+		},
+		"kobo": {
+			Source:    "kobo",
+			Timestamp: ts,
+			Data: map[string]interface{}{
+				"percentage": 0.42,
+			},
+		},
+	}
+
+	source, _ := handler.getMostRecentSource(conflictData)
+	assert.Contains(t, []string{"koreader", "kobo"}, source)
+}
+
+func TestGetMostRecentSource_EmptyData(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{}
+
+	source, data := handler.getMostRecentSource(conflictData)
+	assert.Equal(t, "", source)
+	assert.Nil(t, data)
+}
+
+func TestGetHighestProgressSource_KOReaderHigher(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source: "koreader",
+			Data: map[string]interface{}{
+				"percentage": 0.75,
+			},
+		},
+		"kobo": {
+			Source: "kobo",
+			Data: map[string]interface{}{
+				"percentage": 0.42,
+			},
+		},
+	}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.Equal(t, "koreader", source)
+	assert.Equal(t, 0.75, data["percentage"])
+}
+
+func TestGetHighestProgressSource_KoboHigher(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source: "koreader",
+			Data: map[string]interface{}{
+				"percentage": 0.30,
+			},
+		},
+		"kobo": {
+			Source: "kobo",
+			Data: map[string]interface{}{
+				"percentage": 0.90,
+			},
+		},
+	}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.Equal(t, "kobo", source)
+	assert.Equal(t, 0.90, data["percentage"])
+}
+
+func TestGetHighestProgressSource_SingleSource(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source: "koreader",
+			Data: map[string]interface{}{
+				"percentage": 0.50,
+			},
+		},
+	}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.Equal(t, "koreader", source)
+	assert.Equal(t, 0.50, data["percentage"])
+}
+
+func TestGetHighestProgressSource_EmptyData(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.Equal(t, "", source)
+	assert.Nil(t, data)
+}
+
+func TestGetHighestProgressSource_NoPercentageField(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source: "koreader",
+			Data:   map[string]interface{}{},
+		},
+	}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.Equal(t, "", source)
+	assert.Nil(t, data)
+}
+
+func TestGetHighestProgressSource_MixedPercentageTypes(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source: "koreader",
+			Data: map[string]interface{}{
+				"percentage": 0.60,
+			},
+		},
+		"kobo": {
+			Source: "kobo",
+			Data: map[string]interface{}{
+				"percentage": float64(0.80),
+			},
+		},
+	}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.Equal(t, "kobo", source)
+	assert.Equal(t, float64(0.80), data["percentage"])
+}
+
+func TestGetHighestProgressSource_BothZero(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source: "koreader",
+			Data: map[string]interface{}{
+				"percentage": 0.0,
+			},
+		},
+		"kobo": {
+			Source: "kobo",
+			Data: map[string]interface{}{
+				"percentage": 0.0,
+			},
+		},
+	}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.NotEmpty(t, source)
+	assert.NotNil(t, data)
+	assert.Equal(t, 0.0, data["percentage"])
+}
+
+func TestGetHighestProgressSource_ThreeWayConflict(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source: "koreader",
+			Data: map[string]interface{}{
+				"percentage": 0.45,
+			},
+		},
+		"kobo": {
+			Source: "kobo",
+			Data: map[string]interface{}{
+				"percentage": 0.92,
+			},
+		},
+		"web": {
+			Source: "web",
+			Data: map[string]interface{}{
+				"percentage": 0.70,
+			},
+		},
+	}
+
+	source, data := handler.getHighestProgressSource(conflictData)
+	assert.Equal(t, "kobo", source)
+	assert.Equal(t, 0.92, data["percentage"])
+}
+
+func TestGetMostRecentSource_ThreeWayConflict(t *testing.T) {
+	handler := &ConflictHandler{}
+
+	conflictData := map[string]ConflictSourceData{
+		"koreader": {
+			Source:    "koreader",
+			Timestamp: time.Date(2026, 1, 30, 20, 5, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.45,
+			},
+		},
+		"kobo": {
+			Source:    "kobo",
+			Timestamp: time.Date(2026, 1, 30, 20, 20, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.92,
+			},
+		},
+		"web": {
+			Source:    "web",
+			Timestamp: time.Date(2026, 1, 30, 20, 10, 0, 0, time.UTC),
+			Data: map[string]interface{}{
+				"percentage": 0.70,
+			},
+		},
+	}
+
+	source, data := handler.getMostRecentSource(conflictData)
+	assert.Equal(t, "kobo", source)
+	assert.Equal(t, 0.92, data["percentage"])
+}