Hold every declaration to a symbol MEOS exports

MEOS.NET.Tests/NativeSymbolTests.cs

@@ -0,0 +1,64 @@
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+using MEOS.NET.Functions;
+
+namespace MEOS.NET.Tests
+{
+    /// <summary>
+    /// Every function this binding declares must be a symbol the MEOS it loads
+    /// exports.
+    ///
+    /// A P/Invoke binds by name at the first call, so a function MEOS renames or
+    /// drops is invisible to the compiler and reaches a caller as an
+    /// <see cref="EntryPointNotFoundException"/> at run time. Resolving every
+    /// declared entry point against the loaded library turns that into one named
+    /// failure here.
+    /// </summary>
+    [TestClass]
+    public class NativeSymbolTests : MeosTest
+    {
+        [TestMethod]
+        public void EveryDeclaredEntryPointResolvesInTheLoadedMeos()
+        {
+            string[] entryPoints = DeclaredEntryPoints();
+
+            // A parity check that read no declaration would pass over anything.
+            Assert.IsTrue(entryPoints.Length > 1000,
+                $"only {entryPoints.Length} entry points were read from the binding");
+
+            IntPtr meos = NativeLibrary.Load("meos", typeof(Meos).Assembly, null);
+            List<string> missing = entryPoints
+                .Where(name => !NativeLibrary.TryGetExport(meos, name, out _))
+                .ToList();
+
+            Assert.AreEqual(0, missing.Count,
+                $"MEOS exports none of: {string.Join(", ", missing.Take(20))}");
+        }
+
+        [TestMethod]
+        public void ASymbolMeosDoesNotExportIsSeenAsMissing()
+        {
+            IntPtr meos = NativeLibrary.Load("meos", typeof(Meos).Assembly, null);
+
+            Assert.IsFalse(NativeLibrary.TryGetExport(meos, "meos_no_such_function", out _));
+            Assert.IsTrue(NativeLibrary.TryGetExport(meos, "meos_initialize", out _));
+        }
+
+        /// <summary>The entry point of every native declaration the binding carries.</summary>
+        private static string[] DeclaredEntryPoints()
+        {
+            Type native = typeof(Meos).GetNestedType("Native", BindingFlags.NonPublic)
+                ?? throw new InvalidOperationException("the binding declares no Native class");
+
+            return native
+                .GetMethods(BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic
+                    | BindingFlags.DeclaredOnly)
+                .Select(method => method.GetCustomAttribute<LibraryImportAttribute>())
+                .Where(attribute => attribute is not null)
+                .Select(attribute => attribute!.EntryPoint!)
+                .Distinct()
+                .ToArray();
+        }
+    }
+}