Test fixes

Author: paulirwin

src/Lucene.Net.Tests/Store/TestMultiMMap.cs

@@ -2613,13 +2613,13 @@ public void TestOpenSlice_OutOfBounds_Throws()
             using var slicer = mmapDir.CreateSlicer("f", NewIOContext(Random));
 
             // Negative offset.
-            Assert.Throws<ArgumentException>(() => slicer.OpenSlice("neg-off", -1, 4));
+            Assert.Throws<ArgumentOutOfRangeException>(() => slicer.OpenSlice("neg-off", -1, 4));
             // Negative length.
-            Assert.Throws<ArgumentException>(() => slicer.OpenSlice("neg-len", 0, -1));
+            Assert.Throws<ArgumentOutOfRangeException>(() => slicer.OpenSlice("neg-len", 0, -1));
             // offset + length past end of file.
-            Assert.Throws<ArgumentException>(() => slicer.OpenSlice("past-end", 8, 10));
+            Assert.Throws<ArgumentOutOfRangeException>(() => slicer.OpenSlice("past-end", 8, 10));
             // offset alone past end of file.
-            Assert.Throws<ArgumentException>(() => slicer.OpenSlice("off-past-end", 17, 0));
+            Assert.Throws<ArgumentOutOfRangeException>(() => slicer.OpenSlice("off-past-end", 17, 0));
 
             // Edge: offset == length == 0 is fine on a non-empty file.
             using (var s = slicer.OpenSlice("empty", 0, 0)) { Assert.AreEqual(0L, s.Length); }

src/Lucene.Net/Store/MMapDirectory.cs

@@ -246,7 +246,8 @@ public IndexInputSlicerAnonymousClass(MMapDirectory outerInstance, string file,
             public override IndexInput OpenSlice(string? sliceDescription, long offset, long length)
             {
                 outerInstance.EnsureOpen();
-                if ((ulong)offset >= (ulong)mapping.Length)
+                // LUCENENET NOTE: TestSeekSliceZero invariant allows 0 offset with 0 length
+                if (offset != 0 && (ulong)offset >= (ulong)mapping.Length)
                     throw new ArgumentOutOfRangeException(nameof(offset),
                         $"slice() {sliceDescription ?? "(null)"} offset out of bounds: " +
                         $"offset={offset},length={length},fileLength={mapping.Length}: {this}");