Add test case

src/main/scala/minisql/Quoted.scala

@@ -179,6 +179,8 @@ object Query {
 
     inline def max: Agg[Long] = Aggregation(AggregationOperator.max, e)
 
+    inline def sum: Agg[Option[E]] = Aggregation(AggregationOperator.sum, e)
+
   }
 }
 

src/test/scala/minisql/context/sql/MirrorSqlContextSuite.scala

@@ -177,4 +177,12 @@ class MirrorSqlContextSuite extends munit.FunSuite {
       "SELECT MAX(f.age) FROM foo f"
     )
   }
+
+  test("Aggregations - max") {
+    val o = testContext.io(Foos.map(f => f.age).sum)
+    assertEquals(
+      o.sql,
+      "SELECT SUM(f.age) FROM foo f"
+    )
+  }
 }