fix: issues from static code analysis

Source/Testably.Expectations/Core/Ambient/Initialization.cs

@@ -57,7 +57,7 @@ public InitializationState(ITestFrameworkAdapter testFramework)
 		public void Throw(string message) => _testFramework.Throw(message);
 	}
 
-	private class FallbackTestFramework : ITestFrameworkAdapter
+	private sealed class FallbackTestFramework : ITestFrameworkAdapter
 	{
 		#region ITestFrameworkAdapter Members
 

Source/Testably.Expectations/Core/ExpectationBuilders/WhichExpectationBuilder.cs

@@ -57,7 +57,7 @@ public ExpectationResult ApplyTo<TExpectation>(TExpectation actual)
 
 	public static object? GetPropertyValue(object? obj, string propertyPath)
 	{
-		if (propertyPath.IndexOf(".", StringComparison.Ordinal) < 0)
+		if (propertyPath.IndexOf('.', StringComparison.Ordinal) < 0)
 		{
 			Type? objType = obj?.GetType();
 			return objType?.GetProperty(propertyPath)?.GetValue(obj, null);

Source/Testably.Expectations/Core/ShouldVerb.cs

@@ -11,7 +11,7 @@ public abstract class ShouldVerb
 {
 	private readonly IExpectationBuilderStart _expectationBuilder;
 
-	internal ShouldVerb(IExpectationBuilderStart expectationBuilder)
+	private protected ShouldVerb(IExpectationBuilderStart expectationBuilder)
 	{
 		_expectationBuilder = expectationBuilder;
 	}
@@ -40,17 +40,17 @@ public ExpectationWhichShould<T1, T2> WithExpectation<T1, T2>(
 
 	#pragma warning disable CS0809
 	/// <inheritdoc />
-	[Obsolete]
+	[Obsolete("Equals is not part of Testably.Expectations.")]
 	[EditorBrowsable(EditorBrowsableState.Never)]
 	public override bool Equals(object? obj)
-		=> throw new NotSupportedException(
-			"Equals is not part of Testably.Expectations.");
+		// ReSharper disable once BaseObjectEqualsIsObjectEquals
+		=> base.Equals(obj);
 
 	/// <inheritdoc />
-	[Obsolete]
+	[Obsolete("Equals is not part of Testably.Expectations.")]
 	[EditorBrowsable(EditorBrowsableState.Never)]
 	public override int GetHashCode()
-		=> throw new NotSupportedException(
-			"Equals is not part of Testably.Expectations.");
-	#pragma warning restore CS0809
+		// ReSharper disable once BaseObjectGetHashCodeCallInGetHashCode
+		=> base.GetHashCode();
+#pragma warning restore CS0809
 }

Source/Testably.Expectations/Polyfills/StringExtensions.cs

@@ -0,0 +1,28 @@
+#if NETSTANDARD2_0
+using System;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Testably.Expectations.Polyfills;
+
+/// <summary>
+///     Provides extension methods to simplify writing platform independent tests.
+/// </summary>
+[ExcludeFromCodeCoverage]
+internal static class StringExtensionMethods
+{
+	/// <summary>
+	///     Reports the zero-based index of the first occurrence of the specified Unicode character in this string. A parameter
+	///     specifies the type of search to use for the specified character.
+	/// </summary>
+	/// <returns>
+	///     The zero-based index of <paramref name="value" /> if that character is found, or <c>-1</c> if it is not.
+	/// </returns>
+	internal static int IndexOf(
+		this string @this,
+		char value,
+		StringComparison comparisonType)
+	{
+		return @this.IndexOf($"{value}", comparisonType);
+	}
+}
+#endif

Source/Testably.Expectations/Usings.cs

@@ -0,0 +1,3 @@
+#if NETSTANDARD2_0 || NETSTANDARD2_1
+global using Testably.Expectations.Polyfills;
+#endif