Source: Correct way to load assembly

If you do not have access to the TestRunner type information in the calling assembly (it sounds like you may not), you can call the method like this:

Assembly assembly = Assembly.LoadFile(@"C:\dyn.dll");
Type     type     = assembly.GetType("TestRunner");
var      obj      = Activator.CreateInstance(type);
 
// Alternately you could get the MethodInfo for the TestRunner.Run method
type.InvokeMember("Run", 
                  BindingFlags.Default | BindingFlags.InvokeMethod, 
                  null,
                  obj,
                  null);

If you have access to the IRunnable interface type, you can cast your instance to that (rather than the TestRunner type, which is implemented in the dynamically created or loaded assembly, right?):

  Assembly assembly  = Assembly.LoadFile(@"C:\dyn.dll");  // @ = static string, i.e. no special char interpretation in the following string
  Type     type      = assembly.GetType("TestRunner");
  IRunnable runnable = Activator.CreateInstance(type) as IRunnable;
  if (runnable == null) throw new Exception("broke");
  runnable.Run();

Create a library wrapper to reference from your managed code.

• Import library function signatures. Open a Visual Studio Command Prompt and issue this command:

  C:\> dumpbin /exports MyLib.dll

  This outputs:

  Dump of file MyLib.dll
  
  File Type: DLL
  
    Section contains the following exports for MyLib.dll
  
      00000000 characteristics
             0 time date stamp Wed Dec 31 19:00:00 1969
          0.00 version
             1 ordinal base
            17 number of functions
            17 number of names
  
      ordinal hint RVA      name
  
            1    0 00010D4C Initialize
            2    1 00010D5C ActivateDevice
           15    2 000112F8 OpenPort
            4    3 00010F94 ClosePort
           14    4 000111F4 GetDebugStatus
           12    5 0001131C GetFcomVersion
           11    6 00010FCC GetNoPollTimeout
           17    7 000113B0 GetPortMode
            5    8 0001102C GetPortStatus
            9    9 00010E98 GetRspArray
           13    A 0001133C MaxComPort
            3    B 00010ECC OpenPort
            8    C 00010E74 RspReady
            7    D 00010E40 SendCmdArray
            6    E 00010D6C SendReady
           10    F 00011004 SetNoPollTimeout
           16   10 0001135C SetPortMode
  
    Summary
  
          1000 .edata
          1000 .idata
          2000 .reloc
          2000 .rsrc
          2000 BSS
         11000 CODE
          1000 DATA

• Create wrapper with each function name found with dumpbin using DllImport:

  using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Runtime.InteropServices;
   
  namespace AHI.Testing.Frye
  {
      public class MyLib_DLL_Wrapper
      {
          private const String DLL_NAME = "MyLib.dll";  // DLL
          [DllImport(DLL_NAME, EntryPoint = "OpenPort")]
          public static extern int OpenPort(ref int portNum);
   
          [DllImport(DLL_NAME, EntryPoint = "ClosePort")]
          public static extern int ClosePort(ref int portNum);
          ...
      }
  }