Add test

Author: YegorStepanov

tests/BenchmarkDotNet.Tests/Validators/ExecutionValidatorTests.cs

@@ -317,6 +317,33 @@ public class NonPublicFieldWithParams
             public void NonThrowing() { }
         }
 
+        [Fact]
+        public void NonPublicFieldsWithParamsSourceAreDiscovered()
+        {
+            var validationErrors = ExecutionValidator.FailOnError
+                .Validate(BenchmarkConverter.TypeToBenchmarks(typeof(NonPublicFieldWithParamsSource)))
+                .ToList();
+
+            Assert.NotEmpty(validationErrors);
+            Assert.StartsWith($"Member \"{nameof(NonPublicFieldWithParamsSource.Field)}\" must be public if it has the [ParamsSource]", validationErrors.Single().Message);
+        }
+
+        public class NonPublicFieldWithParamsSource
+        {
+#pragma warning disable CS0649
+            [ParamsSource(nameof(Get))]
+            internal int Field;
+#pragma warning restore CS0649
+
+            [Benchmark]
+            public void NonThrowing() { }
+
+            public IEnumerable<object> Get()
+            {
+                yield return 0;
+            }
+        }
+
         [Fact]
         public void NonPublicPropertiesWithParamsAreDiscovered()
         {