Address PR feedback

src/libraries/System.Net.Http/src/System/Net/Http/Headers/ObjectCollection.cs

@@ -94,7 +94,7 @@ public void Clear()
         }
 
         public bool Contains(T item) =>
-            _size == 0 || _items is null ? false :
+            _size <= 0 ? false :
             _items is T o ? o.Equals(item) :
             _items is T[] items && Array.IndexOf(items, item, 0, _size) != -1;
 
@@ -121,14 +121,16 @@ public void CopyTo(T[] array, int arrayIndex)
 
         public bool Remove(T item)
         {
-            if (_items is T o && o.Equals(item))
+            if (_items is T o)
             {
-                _items = null;
-                _size = 0;
-                return true;
+                if (o.Equals(item))
+                {
+                    _items = null;
+                    _size = 0;
+                    return true;
+                }
             }
-
-            if (_items is T[] items)
+            else if (_items is T[] items)
             {
                 int index = Array.IndexOf(items, item, 0, _size);
                 if (index != -1)

src/libraries/System.Net.Http/tests/UnitTests/Headers/ObjectCollectionTest.cs

@@ -41,24 +41,69 @@ public void Ctor_ExecuteBothOverloads_MatchExpectation()
         [Fact]
         public void ContainsAndRemove_UsesEqualitySemantics()
         {
-            // Use default validator
             ObjectCollection<string> c = new ObjectCollection<string>();
 
+            string val1 = "value1";
+            string val1DifferentReference = "value" + 1;
+            Assert.NotSame(val1, val1DifferentReference);
+            Assert.Equal(val1, val1DifferentReference);
+
+            string val2 = "value2";
+            string val2DifferentReference = "value" + 2;
+            Assert.NotSame(val2, val2DifferentReference);
+            Assert.Equal(val2, val2DifferentReference);
+
+            string val3 = "value3";
+
+            // Start empty
+            Assert.Equal(0, c.Count);
+            Assert.False(c.Contains(val1));
+
+            // Single item
+            c.Add(val1);
+            Assert.Equal(1, c.Count);
+            Assert.True(c.Contains(val1));
+            Assert.True(c.Contains(val1DifferentReference));
+            Assert.False(c.Contains(val2));
+
+            // Single item removal
+            Assert.True(c.Remove(val1));
             Assert.Equal(0, c.Count);
-            Assert.False(c.Contains("value" + 1));
+            Assert.False(c.Contains(val1));
 
-            c.Add("value" + 1);
+            // Multi-value
+            c.Add(val1);
+            c.Add(val2);
+            Assert.Equal(2, c.Count);
+            Assert.True(c.Contains(val1));
+            Assert.True(c.Contains(val1DifferentReference));
+            Assert.True(c.Contains(val2));
+            Assert.True(c.Contains(val1DifferentReference));
+            Assert.False(c.Contains(val3));
 
+            // Removal when multiple exist, using different reference.
+            Assert.True(c.Remove(val1));
+            Assert.False(c.Contains(val1));
+            Assert.True(c.Contains(val2));
             Assert.Equal(1, c.Count);
-            // Force the reference to be different to ensure we are checking for semantic equality
-            // and not reference equality.
-            Assert.True(c.Contains("value" + 1));
-            c.Add("value" + 2);
 
-            Assert.True(c.Remove("value" + 1));
+            // Removal of non-existent
+            Assert.False(c.Remove(val3));
+            Assert.False(c.Remove(val1DifferentReference));
             Assert.Equal(1, c.Count);
+            Assert.True(c.Contains(val2DifferentReference));
 
-            Assert.True(c.Contains("value" + 2));
+            // Removal last item
+            Assert.True(c.Remove(val2DifferentReference));
+            Assert.Equal(0, c.Count);
+            Assert.False(c.Contains(val2));
+            Assert.False(c.Contains(val1));
+
+            // Remove from empty
+            Assert.False(c.Remove(val1));
+            Assert.False(c.Remove(val2));
+            Assert.False(c.Remove(val3));
+            Assert.Equal(0, c.Count);
         }
     }
 }