diff --git a/spatial-index/codepoint.go b/spatial-index/codepoint.go
index a763868..d66ee50 100644
--- a/spatial-index/codepoint.go
+++ b/spatial-index/codepoint.go
@@ -20,6 +20,19 @@ type SpatialIndex struct {
 	tree *rtree.RTreeGN[uint32, string]
 }
 
+func NewCodePointSpatialIndex(zipFile string) (*SpatialIndex, error) {
+	idx := SpatialIndex{
+		tree: &rtree.RTreeGN[uint32, string]{},
+	}
+
+	err := idx.importCodePoint(zipFile)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load codepoint index from zip file: %w", err)
+	}
+
+	return &idx, nil
+}
+
 func (idx *SpatialIndex) Search(bounds []uint32) (*[]CodePoint, error) {
 
 	results := make([]CodePoint, 0, 100)
@@ -51,19 +64,6 @@ func (idx *SpatialIndex) SearchIter(bounds []uint32, iter func(min, max [2]uint3
 	return nil
 }
 
-func NewCodePointSpatialIndex(zipFile string) (*SpatialIndex, error) {
-	idx := SpatialIndex{
-		tree: &rtree.RTreeGN[uint32, string]{},
-	}
-
-	err := idx.importCodePoint(zipFile)
-	if err != nil {
-		return nil, fmt.Errorf("failed to load codepoint index from zip file: %w", err)
-	}
-
-	return &idx, nil
-}
-
 func (idx *SpatialIndex) Len() int {
 	return idx.tree.Len()
 }
diff --git a/spatial-index/codepoint_test.go b/spatial-index/codepoint_test.go
new file mode 100644
index 0000000..3806651
--- /dev/null
+++ b/spatial-index/codepoint_test.go
@@ -0,0 +1,103 @@
+package spatialindex
+
+import (
+	"archive/zip"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/rtree"
+)
+
+func createTestZip(t *testing.T, files map[string]string) string {
+	t.Helper()
+	tmpfile, err := os.CreateTemp("", "test-*.zip")
+	require.NoError(t, err, "failed to create temp file")
+	defer func() { _ = tmpfile.Close() }()
+
+	w := zip.NewWriter(tmpfile)
+	for name, content := range files {
+		f, err := w.Create(name)
+		require.NoError(t, err, "failed to create file in zip")
+		_, err = f.Write([]byte(content))
+		require.NoError(t, err, "failed to write file in zip")
+	}
+	_ = w.Close()
+	return tmpfile.Name()
+}
+
+func TestNewCodePointSpatialIndex_Success(t *testing.T) {
+	csv := "PC1,PC2,123,456\nPC3,PC4,789,1011\n"
+	zipPath := createTestZip(t, map[string]string{"Data/CSV/test.csv": csv})
+	defer func() { _ = os.Remove(zipPath) }()
+
+	idx, err := NewCodePointSpatialIndex(zipPath)
+	require.NoError(t, err)
+	require.Equal(t, 2, idx.Len())
+}
+
+func TestNewCodePointSpatialIndex_BadZip(t *testing.T) {
+	_, err := NewCodePointSpatialIndex("/no/such/file.zip")
+	require.Error(t, err, "failed to open zip file: file does not exist")
+}
+
+func TestSearch(t *testing.T) {
+	csv := "PC1,PC2,100,200\nPC2,PC3,300,400\n"
+	zipPath := createTestZip(t, map[string]string{"Data/CSV/test.csv": csv})
+	defer func() { _ = os.Remove(zipPath) }()
+	idx, err := NewCodePointSpatialIndex(zipPath)
+	require.NoError(t, err)
+
+	// Search for both
+	res, err := idx.Search([]uint32{0, 0, 500, 500})
+	require.NoError(t, err)
+	require.Equal(t, 2, len(*res))
+
+	// Search for one
+	res, err = idx.Search([]uint32{90, 190, 110, 210})
+	require.NoError(t, err)
+	require.Equal(t, 1, len(*res))
+	require.Equal(t, "PC1", (*res)[0].PostCode)
+
+	// Search for none
+	res, err = idx.Search([]uint32{1000, 1000, 2000, 2000})
+	require.NoError(t, err)
+	require.Equal(t, 0, len(*res))
+}
+
+func TestSearchIter_InvalidBounds(t *testing.T) {
+	idx := &SpatialIndex{tree: &rtree.RTreeGN[uint32, string]{}}
+	err := idx.SearchIter([]uint32{1, 2, 3}, func([2]uint32, [2]uint32, string) bool { return true })
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "bounds must contain exactly 4 values")
+}
+
+func TestLen(t *testing.T) {
+	csv := "PC1,PC2,1,2\nPC2,PC3,3,4\nPC3,PC4,5,6\n"
+	zipPath := createTestZip(t, map[string]string{"Data/CSV/test.csv": csv})
+	defer func() { _ = os.Remove(zipPath) }()
+	idx, err := NewCodePointSpatialIndex(zipPath)
+	require.NoError(t, err)
+	require.Equal(t, 3, idx.Len())
+}
+
+func Test_fromCodePointCSV(t *testing.T) {
+	rec := []string{"PC1", "PC2", "123", "456"}
+	cp, err := fromCodePointCSV(rec, nil)
+	require.NoError(t, err)
+	require.Equal(t, "PC1", cp.PostCode)
+	require.Equal(t, uint32(123), cp.Easting)
+	require.Equal(t, uint32(456), cp.Northing)
+
+	// Bad easting
+	rec = []string{"PC1", "PC2", "bad", "456"}
+	_, err = fromCodePointCSV(rec, nil)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "easting")
+
+	// Bad northing
+	rec = []string{"PC1", "PC2", "123", "bad"}
+	_, err = fromCodePointCSV(rec, nil)
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "northing")
+}