Add more backend unit tests

backend/internal/util/time_test.go

@@ -0,0 +1,25 @@
+package util
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUnixMilliToNiceFormat(t *testing.T) {
+	tests := []struct {
+		input    int64
+		expected string
+	}{
+		{0, "1970-01-01 10:00:00"},                   // Unix epoch time
+		{1568000000000, "2019-09-09 13:33:20"},       // Arbitrary millisecond timestamp
+		{1636598400000, "2021-11-11 12:40:00"},       // Another arbitrary millisecond timestamp
+		{-1000000000000, "1938-04-25 08:13:20"},      // Negative millisecond timestamp
+		{9223372036854775807, "1970-01-01 09:59:59"}, // Maximum representable millisecond timestamp
+	}
+
+	for _, test := range tests {
+		output := UnixMilliToNiceFormat(test.input)
+		assert.Equal(t, test.expected, output)
+	}
+}