Re-land BindingContext.PropertyType regression test on master

src/Tests/ExistForAll.SimpleSettings.UnitTests/SimpleSettings/BindingContextTests.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+
+namespace ExistForAll.SimpleSettings.UnitTests.SimpleSettings
+{
+	public class BindingContextTests
+	{
+		[Test]
+		public async Task BindPropertySettings_ContextPropertyType_IsThePropertysOwnType()
+		{
+			var binder = new CapturingBinder();
+
+			SettingsBuilder.CreateBuilder(x => x.AddSectionBinder(binder))
+				.GetSettings<ICaptureSettings>();
+
+			// PropertyType must be each property's own type — not the declaring interface
+			// (regression guard: it was previously set to propertyInfo.DeclaringType).
+			await Assert.That(binder.Captured[nameof(ICaptureSettings.Name)].PropertyType).IsEqualTo(typeof(string));
+			await Assert.That(binder.Captured[nameof(ICaptureSettings.Count)].PropertyType).IsEqualTo(typeof(int));
+		}
+
+		[Test]
+		public async Task BindPropertySettings_ContextStillExposesDeclaringInterface()
+		{
+			var binder = new CapturingBinder();
+
+			SettingsBuilder.CreateBuilder(x => x.AddSectionBinder(binder))
+				.GetSettings<ICaptureSettings>();
+
+			var context = binder.Captured[nameof(ICaptureSettings.Name)];
+
+			// Fixing PropertyType did not remove access to the declaring type: the settings
+			// interface is on SettingsType, and the property's declaring type on PropertyInfo.
+			await Assert.That(context.SettingsType).IsEqualTo(typeof(ICaptureSettings));
+			await Assert.That(context.PropertyInfo.DeclaringType).IsEqualTo(typeof(ICaptureSettings));
+		}
+
+		private sealed class CapturingBinder : ISectionBinder
+		{
+			public Dictionary<string, BindingContext> Captured { get; } = new Dictionary<string, BindingContext>();
+
+			public void BindPropertySettings(BindingContext context)
+			{
+				Captured[context.Key] = context;
+			}
+		}
+
+		public interface ICaptureSettings
+		{
+			string Name { get; set; }
+			int Count { get; set; }
+		}
+	}
+}