Add tests for renderLines

These are very simple yet, but we'll extend them in the next commits.

pkg/gui/context/list_renderer_test.go

@@ -0,0 +1,74 @@
+package context
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/samber/lo"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestListRenderer_renderLines(t *testing.T) {
+	scenarios := []struct {
+		name           string
+		modelStrings   []string
+		startIdx       int
+		endIdx         int
+		expectedOutput string
+	}{
+		{
+			name:         "Render whole list",
+			modelStrings: []string{"a", "b", "c"},
+			startIdx:     0,
+			endIdx:       3,
+			expectedOutput: `
+				a
+				b
+				c`,
+		},
+		{
+			name:         "Partial list, beginning",
+			modelStrings: []string{"a", "b", "c"},
+			startIdx:     0,
+			endIdx:       2,
+			expectedOutput: `
+				a
+				b`,
+		},
+		{
+			name:         "Partial list, end",
+			modelStrings: []string{"a", "b", "c"},
+			startIdx:     1,
+			endIdx:       3,
+			expectedOutput: `
+				b
+				c`,
+		},
+		{
+			name:         "Pass an endIdx greater than the model length",
+			modelStrings: []string{"a", "b", "c"},
+			startIdx:     2,
+			endIdx:       5,
+			expectedOutput: `
+				c`,
+		},
+	}
+	for _, s := range scenarios {
+		t.Run(s.name, func(t *testing.T) {
+			viewModel := NewListViewModel[string](func() []string { return s.modelStrings })
+			self := &ListRenderer{
+				list: viewModel,
+				getDisplayStrings: func(startIdx int, endIdx int) [][]string {
+					return lo.Map(s.modelStrings[startIdx:endIdx],
+						func(s string, _ int) []string { return []string{s} })
+				},
+			}
+
+			expectedOutput := strings.Join(lo.Map(
+				strings.Split(strings.TrimPrefix(s.expectedOutput, "\n"), "\n"),
+				func(line string, _ int) string { return strings.TrimSpace(line) }), "\n")
+
+			assert.Equal(t, expectedOutput, self.renderLines(s.startIdx, s.endIdx))
+		})
+	}
+}