Tests to YEAR TO MONTH type and fix for the comparison

src/deveeldb-nunit/Deveel.Data.Sql.Objects/SqlIntervalTests.cs

@@ -130,5 +130,38 @@ public class SqlIntervalTests {
 
 			Assert.AreEqual(1, result);
 		}
+
+		[TestCase(22, 1)]
+		[Category("Year To Month")]
+		[Category("Conversion")]
+		public void YearToMonthFromInteger(int months, int expectedYears) {
+			var value = new SqlYearToMonth(months);
+
+			Assert.IsNotNull(value);
+			Assert.IsFalse(value.IsNull);
+
+			Assert.AreEqual(expectedYears, (int) value.TotalYears);
+		}
+
+		[Test]
+		[Category("Year To Month")]
+		public void CompareYearToMonths() {
+			var value1 = new SqlYearToMonth(22);
+			var value2 = new SqlYearToMonth(1, 2);
+
+			var result = value1.CompareTo(value2);
+			Assert.AreEqual(1, result);
+		}
+
+		[Test]
+		[Category("Year To Month")]
+		public void CompareYearToMonthToNull() {
+			var value1 = new SqlYearToMonth(22);
+			var value2 = SqlYearToMonth.Null;
+
+			var result = value1.CompareTo(value2);
+
+			Assert.AreEqual(1, result);
+		}
 	}
 }

src/deveeldb/Deveel.Data.Sql.Objects/SqlYearToMonth.cs

@@ -92,9 +92,9 @@ private SqlYearToMonth(bool isNull)
 			if (other.IsNull && IsNull)
 				return 0;
 			if (IsNull && !other.IsNull)
-				return 1;
-			if (!IsNull && other.IsNull)
 				return -1;
+			if (!IsNull && other.IsNull)
+				return 1;
 
 			return months.Value.CompareTo(other.months.Value);
 		}