Moved logic of collapsing songs into albums to model package

(it should really be called domain.... maybe will rename it later)

utils/slice/slice_test.go

@@ -0,0 +1,43 @@
+package slice_test
+
+import (
+	"testing"
+
+	"github.com/navidrome/navidrome/utils/slice"
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestSlice(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Slice Suite")
+}
+
+var _ = Describe("Group", func() {
+	It("returns empty map for an empty input", func() {
+		keyFunc := func(v int) int { return v % 2 }
+		result := slice.Group([]int{}, keyFunc)
+		Expect(result).To(BeEmpty())
+	})
+
+	It("groups by the result of the key function", func() {
+		keyFunc := func(v int) int { return v % 2 }
+		result := slice.Group([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}, keyFunc)
+		Expect(result).To(HaveLen(2))
+		Expect(result[0]).To(ConsistOf(2, 4, 6, 8, 10))
+		Expect(result[1]).To(ConsistOf(1, 3, 5, 7, 9, 11))
+	})
+})
+
+var _ = Describe("MostFrequent", func() {
+	It("returns zero value if no arguments are passed", func() {
+		Expect(slice.MostFrequent([]int{})).To(BeZero())
+	})
+
+	It("returns the single item", func() {
+		Expect(slice.MostFrequent([]string{"123"})).To(Equal("123"))
+	})
+	It("returns the item that appeared more times", func() {
+		Expect(slice.MostFrequent([]string{"1", "2", "1", "2", "3", "2"})).To(Equal("2"))
+	})
+})