Fix SkipUntil to not call MoveNext past end of sequence

This is a squashed merge of PR #666 that closes #664.

Author: Orace

MoreLinq.Test/SkipUntilTest.cs

@@ -18,6 +18,8 @@
 namespace MoreLinq.Test
 {
     using NUnit.Framework;
+    using NUnit.Framework.Interfaces;
+    using System.Collections.Generic;
 
     [TestFixture]
     public class SkipUntilTest
@@ -57,5 +59,25 @@ public void SkipUntilEvaluatesPredicateLazily()
             var sequence = Enumerable.Range(-2, 5).SkipUntil(x => 1 / x == -1);
             sequence.AssertSequenceEqual(0, 1, 2);
         }
+
+        public static readonly IEnumerable<ITestCaseData> TestData =
+            from e in new[]
+            {
+                new { Source = new int[0]       , Min = 0, Expected = new int[0]     }, // empty sequence
+                new { Source = new[] { 0       }, Min = 0, Expected = new int[0]     }, // one-item sequence, predicate succeed
+                new { Source = new[] { 0       }, Min = 1, Expected = new int[0]     }, // one-item sequence, predicate don't succeed
+                new { Source = new[] { 1, 2, 3 }, Min = 0, Expected = new[] { 2, 3 } }, // predicate succeed on first item
+                new { Source = new[] { 1, 2, 3 }, Min = 1, Expected = new[] { 2, 3 } },
+                new { Source = new[] { 1, 2, 3 }, Min = 2, Expected = new[] { 3    } },
+                new { Source = new[] { 1, 2, 3 }, Min = 3, Expected = new int[0]     }, // predicate succeed on last item
+                new { Source = new[] { 1, 2, 3 }, Min = 4, Expected = new int[0]     }  // predicate never succeed
+            }
+            select new TestCaseData(e.Source, e.Min).Returns(e.Expected);
+
+        [Test, TestCaseSource(nameof(TestData))]
+        public int[] TestSkipUntil(int[] source, int min)
+        {
+            return source.AsTestingSequence().SkipUntil(v => v >= min).ToArray();
+        }
     }
 }

MoreLinq/SkipUntil.cs

@@ -59,16 +59,17 @@ public static IEnumerable<TSource> SkipUntil<TSource>(this IEnumerable<TSource>
 
             return _(); IEnumerable<TSource> _()
             {
-                using var iterator = source.GetEnumerator();
+                using var enumerator = source.GetEnumerator();
 
-                while (iterator.MoveNext())
+                do
                 {
-                    if (predicate(iterator.Current))
-                        break;
+                    if (!enumerator.MoveNext())
+                        yield break;
                 }
+                while (!predicate(enumerator.Current));
 
-                while (iterator.MoveNext())
-                    yield return iterator.Current;
+                while (enumerator.MoveNext())
+                    yield return enumerator.Current;
             }
         }
     }