diff --git a/confsync/tests/test_merge.py b/confsync/tests/test_merge.py
new file mode 100644
index 0000000..b89d2bb
--- /dev/null
+++ b/confsync/tests/test_merge.py
@@ -0,0 +1,209 @@
+"""Tests for merge strategies."""
+
+import pytest
+from confsync.core.merger import (
+    Merger,
+    KeepLocalStrategy,
+    KeepRemoteStrategy,
+    KeepCommonStrategy,
+    ThreeWayMergeStrategy,
+    UnionMergeStrategy,
+    MergeConflict,
+)
+
+
+class TestMergeStrategies:
+    """Tests for individual merge strategies."""
+
+    def test_keep_local_strategy(self):
+        """Test keep local strategy."""
+        strategy = KeepLocalStrategy()
+
+        local = "local content"
+        remote = "remote content"
+
+        success, merged, conflict = strategy.merge(local, remote)
+
+        assert success
+        assert merged == local
+        assert conflict is None
+
+    def test_keep_remote_strategy(self):
+        """Test keep remote strategy."""
+        strategy = KeepRemoteStrategy()
+
+        local = "local content"
+        remote = "remote content"
+
+        success, merged, conflict = strategy.merge(local, remote)
+
+        assert success
+        assert merged == remote
+        assert conflict is None
+
+    def test_keep_common_strategy(self):
+        """Test keep common strategy."""
+        strategy = KeepCommonStrategy()
+
+        local = "line1\nline2\nline3"
+        remote = "line2\nline3\nline4"
+
+        success, merged, conflict = strategy.merge(local, remote)
+
+        assert success
+        assert "line2" in merged
+        assert "line3" in merged
+        assert "line1" not in merged
+        assert "line4" not in merged
+
+    def test_three_way_merge_identical(self):
+        """Test three-way merge with identical content."""
+        strategy = ThreeWayMergeStrategy()
+
+        content = "same content"
+        success, merged, conflict = strategy.merge(content, content, content)
+
+        assert success
+        assert merged == content
+        assert conflict is None
+
+    def test_three_way_merge_no_conflicts(self):
+        """Test three-way merge without conflicts."""
+        strategy = ThreeWayMergeStrategy()
+
+        base = "same content"
+        local = "same content"
+        remote = "same content"
+
+        success, merged, conflict = strategy.merge(local, remote, base)
+
+        assert success
+        assert conflict is None
+
+    def test_union_merge_strategy(self):
+        """Test union merge strategy."""
+        strategy = UnionMergeStrategy()
+
+        local = "line1\nline2\nline3"
+        remote = "line3\nline4\nline5"
+
+        success, merged, conflict = strategy.merge(local, remote)
+
+        assert success
+        assert "line1" in merged
+        assert "line2" in merged
+        assert "line3" in merged
+        assert "line4" in merged
+        assert "line5" in merged
+
+    def test_union_merge_removes_duplicates(self):
+        """Test union merge removes duplicate lines."""
+        strategy = UnionMergeStrategy()
+
+        local = "line1\nline2\nline2"
+        remote = "line2\nline3"
+
+        success, merged, conflict = strategy.merge(local, remote)
+
+        assert success
+        lines = merged.split('\n')
+        assert lines.count("line2") == 1
+
+
+class TestMergeConflict:
+    """Tests for merge conflict handling."""
+
+    def test_format_conflict(self):
+        """Test conflict formatting."""
+        conflict = MergeConflict(
+            file_path="/test/file.txt",
+            local_lines=["local line 1", "local line 2"],
+            remote_lines=["remote line 1", "remote line 2"],
+            base_lines=["base line 1"],
+        )
+
+        formatted = conflict.format_conflict()
+
+        assert "<<<<<<< LOCAL" in formatted
+        assert "=======" in formatted
+        assert ">>>>>>> REMOTE" in formatted
+        assert "local line 1" in formatted
+        assert "remote line 1" in formatted
+
+
+class TestMerger:
+    """Tests for the main Merger class."""
+
+    def test_get_strategy(self):
+        """Test getting strategy by name."""
+        merger = Merger()
+
+        strategy = merger.get_strategy("keep_local")
+        assert isinstance(strategy, KeepLocalStrategy)
+
+        strategy = merger.get_strategy("three_way")
+        assert isinstance(strategy, ThreeWayMergeStrategy)
+
+    def test_merge_file_with_strategy(self):
+        """Test merging a single file with strategy."""
+        merger = Merger()
+
+        local = "local config"
+        remote = "remote config"
+
+        success, merged, conflict = merger.merge_file(
+            local, remote, strategy_name="keep_local"
+        )
+
+        assert success
+        assert merged == "local config"
+
+    def test_merge_multiple_files(self):
+        """Test merging multiple files at once."""
+        merger = Merger()
+
+        files = [
+            {
+                "path": "/test/file1.txt",
+                "local": "local1",
+                "remote": "remote1",
+                "strategy": "keep_local",
+            },
+            {
+                "path": "/test/file2.txt",
+                "local": "local2",
+                "remote": "remote2",
+                "strategy": "keep_remote",
+            },
+        ]
+
+        results = merger.merge_multiple(files)
+
+        assert "/test/file1.txt" in results
+        assert "/test/file2.txt" in results
+
+
+class TestMergeResult:
+    """Tests for merge result model."""
+
+    def test_merge_result_serialization(self):
+        """Test MergeResult serialization."""
+        from confsync.models.config_models import MergeResult
+
+        result = MergeResult(
+            success=True,
+            merged_files={"file1": "merged content"},
+            conflicts={},
+            unresolved=[],
+            strategy_used="three_way",
+            message="Merge successful",
+        )
+
+        data = result.to_dict()
+
+        assert data["success"] is True
+        assert data["strategy_used"] == "three_way"
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])