From 1e43f2a59bba0462494066767fac140601791718 Mon Sep 17 00:00:00 2001
From: mihna123 <mihailonvojinovic@gmail.com>
Date: Sun, 23 Aug 2026 17:47:16 +0200
Subject: listing: implement a service layer stub along with tests

---
 internal/listing/service_test.go | 89 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)
 create mode 100644 internal/listing/service_test.go

(limited to 'internal/listing/service_test.go')

diff --git a/internal/listing/service_test.go b/internal/listing/service_test.go
new file mode 100644
index 0000000..1d555c9
--- /dev/null
+++ b/internal/listing/service_test.go
@@ -0,0 +1,89 @@
+package listing
+
+import (
+	"errors"
+	"log/slog"
+	"os"
+	"slices"
+	"testing"
+)
+
+func TestMain(m *testing.M) {
+	slog.SetDefault(slog.New(slog.DiscardHandler))
+	os.Exit(m.Run())
+}
+
+func TestGetAll(t *testing.T) {
+	mock := NewRepositoryMock()
+	s := New(mock)
+	listings, err := s.GetAll()
+	if err != nil {
+		t.Error(err.Error())
+	}
+
+	if len(listings) != 3 {
+		t.Errorf("Listings lengths don't match. Have %d, want 3",
+			len(listings))
+	}
+}
+
+func TestGetAllWithError(t *testing.T) {
+	mock := &RepositoryMock{err: errors.New("db exploded")}
+	s := New(mock)
+	listings, err := s.GetAll()
+
+	if err == nil {
+		t.Error("No error returned from faulty GetAll call")
+	}
+
+	if listings != nil {
+		t.Error("Listings not nil when returned from faulty GetAll call")
+	}
+}
+
+func TestGetByCategory(t *testing.T) {
+	mock := NewRepositoryMock()
+	s := New(mock)
+
+	listings, err := s.GetByCategory("audi")
+	if err != nil {
+		t.Error(err.Error())
+	}
+
+	if len(listings) != 1 {
+		t.Errorf("Listings by category have wrong length. Have %d, want %d",
+			len(listings), 1)
+	}
+	if !slices.Contains(listings[0].category, "audi") {
+		t.Errorf("Returned listing has wrong category. Have %s, want audi",
+			listings[0].category)
+	}
+}
+
+func TestGetByCategoryNoMatches(t *testing.T) {
+	mock := &RepositoryMock{}
+	s := New(mock)
+
+	listings, err := s.GetByCategory("nonexistantcategory")
+	if err != nil {
+		t.Error(err.Error())
+	}
+
+	if listings != nil {
+		t.Error("Listings should be nil if no category matches")
+	}
+}
+
+func TestGetByCategoryWithError(t *testing.T) {
+	mock := &RepositoryMock{err: errors.New("datacenter hit by asteroid")}
+	s := New(mock)
+
+	listings, err := s.GetByCategory("mercedes")
+	if err == nil {
+		t.Error("Error nil when GetByCategory failed")
+	}
+
+	if listings != nil {
+		t.Error("Listings not nil when GetByCategory failed")
+	}
+}
-- 
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