Harden SheetRange equality semantics and null/type safety

src/GoogleSheetsWrapper.Tests/SheetRangeTests.cs

@@ -180,6 +180,35 @@ public void SheetRangeNoTabNameSingleCellR1C1FormattedCorrectly()
             Assert.That(newRange, Is.EqualTo(range));
         }
 
+        [Test]
+        public void SheetRangeEqualsHandlesNullAndDifferentObjectType()
+        {
+            var range = new SheetRange("Tab", 1, 1, 2, 2);
+
+            Assert.That(range.Equals((SheetRange)null), Is.False);
+            Assert.That(range.Equals((object)null), Is.False);
+            Assert.That(range.Equals("not-a-range"), Is.False);
+        }
+
+        [Test]
+        public void SheetRangeEqualsUsesRangeCoordinatesAndTabName()
+        {
+            var rangeA = new SheetRange("Tab", 1, 1, 2, 2);
+            var rangeB = new SheetRange("Tab", 1, 1, 2, 2);
+            var rangeC = new SheetRange("Tab", 1, 1, 3, 2);
+
+            Assert.That(rangeA.Equals(rangeB), Is.True);
+            Assert.That(rangeA.GetHashCode(), Is.EqualTo(rangeB.GetHashCode()));
+            Assert.That(rangeA.Equals(rangeC), Is.False);
+
+            // Derived notation/flags should not participate in equality
+            var mutated = new SheetRange("Tab", 1, 1, 2, 2);
+            mutated.EndColumn = null;
+            var constructed = new SheetRange("Tab", 1, 1, null, 2);
+
+            Assert.That(mutated.Equals(constructed), Is.True);
+        }
+
         private static void AssertLettersFromColumnID(int columnID, string expectedLetters)
         {
             var result = SheetRange.GetLettersFromColumnID(columnID);

src/GoogleSheetsWrapper/GoogleSheetsWrapper.csproj

@@ -8,7 +8,7 @@
     <PackageProjectUrl>https://github.com/SteveWinward/GoogleSheetsWrapper</PackageProjectUrl>
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <RepositoryUrl>https://github.com/SteveWinward/GoogleSheetsWrapper</RepositoryUrl>
-    <Version>2.0.27</Version>
+    <Version>2.0.28</Version>
     <PackageTags>Google Sheets</PackageTags>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <Description>A simple wrapper library that makes it easier to perform CRUD operations against Google Sheets spreadsheets.</Description>

src/GoogleSheetsWrapper/SheetRange.cs

@@ -266,6 +266,16 @@ public static int GetHashCode(SheetRange obj)
         /// <returns><see langword="true"/> when the ranges are equal; otherwise, <see langword="false"/>.</returns>
         public bool Equals(SheetRange other)
         {
+            if (other is null)
+            {
+                return false;
+            }
+
+            if (ReferenceEquals(this, other))
+            {
+                return true;
+            }
+
             return
                 A1Notation == other.A1Notation &&
                 CanSupportA1Notation == other.CanSupportA1Notation &&
@@ -285,7 +295,7 @@ public bool Equals(SheetRange other)
         /// <returns><see langword="true"/> when the object is an equal range; otherwise, <see langword="false"/>.</returns>
         public override bool Equals(object obj)
         {
-            return Equals((SheetRange)obj);
+            return obj is SheetRange other && Equals(other);
         }
 
         /// <summary>
@@ -299,4 +309,4 @@ public override int GetHashCode()
 
         #endregion
     }
-}
+}