1 files changed, 118 insertions, 0 deletions
diff --git a/columnar/columnar_test.go b/columnar/columnar_test.go
new file mode 100644
index 0000000..17dc964
--- /dev/null
+++ b/columnar/columnar_test.go
@@ -0,0 +1,118 @@
+// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
+// SPDX-License-Identifier: Apache-2.0
+
+package columnar_test
+
+import (
+	"encoding/json"
+	"sync"
+	"testing"
+
+	"go.xyrillian.de/gg/columnar"
+	. "go.xyrillian.de/gg/internal/test"
+	"go.xyrillian.de/gg/jsonmatch"
+)
+
+func testSuccessfulJSONRoundtrip[V any](t *testing.T, list []V, encoded jsonmatch.Diffable) {
+	buf, err := json.Marshal(columnar.List[V](list))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, diff := range encoded.DiffAgainst(buf) {
+		t.Error(diff.String())
+	}
+
+	var unmarshaled columnar.List[V]
+	err = json.Unmarshal(buf, &unmarshaled)
+	if err != nil {
+		t.Fatal(err)
+	}
+	AssertEqual(t, []V(unmarshaled), list)
+}
+
+func TestJSONRoundtripBasic(t *testing.T) {
+	// try the example from the package docstring
+	type Person struct {
+		ID        int    `json:"id"`
+		FirstName string `json:"first_name"`
+		LastName  string `json:"last_name"`
+		Married   bool   `json:"married"`
+	}
+
+	testSuccessfulJSONRoundtrip(t,
+		[]Person{
+			{ID: 1, FirstName: "Alice", LastName: "Allison", Married: false},
+			{ID: 2, FirstName: "Bob", LastName: "Burger", Married: true},
+			{ID: 3, FirstName: "Carol", LastName: "Callagher", Married: true},
+		},
+		jsonmatch.Object{
+			"id":         jsonmatch.Array{1, 2, 3},
+			"first_name": jsonmatch.Array{"Alice", "Bob", "Carol"},
+			"last_name":  jsonmatch.Array{"Allison", "Burger", "Callagher"},
+			"married":    jsonmatch.Array{false, true, true},
+		},
+	)
+}
+
+func TestJSONRoundtripWithSpecialFields(t *testing.T) {
+	type Point struct {
+		X float64 `json:"x"`
+		Y float64 `json:"y"`
+	}
+	type Event struct {
+		*Point    `json:"location"` // embedded field, also with pointer
+		Name      string            // without tag -> uses field name as key
+		nameMutex sync.RWMutex      //nolint:unused // not exported -> ignored
+	}
+
+	testSuccessfulJSONRoundtrip(t,
+		[]Event{
+			{Point: &Point{X: 0, Y: 0}, Name: "origin"},
+			{Point: &Point{X: 2, Y: 4}, Name: "somewhere"},
+		},
+		jsonmatch.Object{
+			"location": jsonmatch.Array{jsonmatch.Object{"x": 0, "y": 0}, jsonmatch.Object{"x": 2, "y": 4}},
+			"Name":     jsonmatch.Array{"origin", "somewhere"},
+		},
+	)
+}
+
+func TestJSONRoundtripResolvesPointers(t *testing.T) {
+	type Record struct {
+		Foo int
+		Bar int
+	}
+	testSuccessfulJSONRoundtrip(t,
+		[]***Record{
+			PointerTo(PointerTo(PointerTo(Record{1, 2}))),
+			PointerTo(PointerTo(PointerTo(Record{2, 4}))),
+			PointerTo(PointerTo(PointerTo(Record{3, 6}))),
+		},
+		jsonmatch.Object{
+			"Foo": jsonmatch.Array{1, 2, 3},
+			"Bar": jsonmatch.Array{2, 4, 6},
+		},
+	)
+}
+
+func TestJSONRoundtripErrors(t *testing.T) {
+	type nothingPublic struct {
+		foo int
+		bar int
+	}
+
+	_, err := json.Marshal(columnar.List[nothingPublic]{{1, 2}})
+	AssertEqual(t, err.Error(), `json: error calling MarshalJSON for type columnar.List[go.xyrillian.de/gg/columnar_test.nothingPublic·5]: columnar_test.nothingPublic has no exported fields`)
+	err = json.Unmarshal([]byte(`{}`), PointerTo(columnar.List[nothingPublic]{}))
+	AssertEqual(t, err.Error(), `columnar_test.nothingPublic has no exported fields`)
+}
+
+func TestJSONUnmarshalFromInconsistentLengths(t *testing.T) {
+	type Record struct {
+		Foo int
+		Bar int
+	}
+
+	err := json.Unmarshal([]byte(`{"Foo":[1,2],"Bar":[3,4,5]}`), PointerTo(columnar.List[Record]{}))
+	AssertEqual(t, err.Error(), `cannot unmarshal from columns with inconsistent lengths [2 3]`)
+}