by Geert
13. January 2012 12:54
I like unit tests. So much that I wrote 1003 for Catel to make sure we don’t introduce bugs when changing code. We also love automation, so we use build scripts to create a new (beta) release, create a nuget package and upload the beta versions including symbols.
Anyway, enough history, let’s get to the problem. This week, I fixed an issue that as soon as a ReflectionTypeLoadException occurred, the successfully loaded types were not used by Catel either. That is wrong, so we fixed it. We always run the unit tests using Resharper and dotCover and all succeeded. However, as soon as we ran the unit tests in msbuild (which uses mstest), 3 unit tests failed. It was about this particular code:
1: public static Type[] GetAllTypesSafely(Assembly assembly, bool logLoaderExceptions)
2: {
3: Argument.IsNotNull("assembly", assembly);
4:
5: Type[] foundAssemblyTypes;
6:
7: try
8: {
9: foundAssemblyTypes = assembly.GetTypes();
10: }
11: catch (ReflectionTypeLoadException typeLoadException)
12: {
13: foundAssemblyTypes = typeLoadException.Types;
14:
15: Log.Warning("A ReflectionTypeLoadException occured, adding all {0} types that were loaded correctly", foundAssemblyTypes.Length);
16:
17: if (logLoaderExceptions)
18: {
19: Log.Warning("The following loading exceptions occurred:");
20: foreach (var error in typeLoadException.LoaderExceptions)
21: {
22: Log.Warning(" " + error.Message);
23: }
24: }
25: }
26:
27: return foundAssemblyTypes;
28: }
According to the documentation, the ReflectionTypeLoaderException.Types contains all the successfully loaded types. However, when running the unit tests (which loads more assemblies into the current AppDomain), the array contained 3 instances of null.
WTF? A successfully loaded type that is null? /*sarcasme on*/ I bet the Microsoft engineers had a good reason for this /*sarcasm off*/. Anyway, I fixed the issue by filtering out the null values. Below is the fixed code (notice the LINQ expression):
1: public static Type[] GetAllTypesSafely(Assembly assembly, bool logLoaderExceptions)
2: {
3: Argument.IsNotNull("assembly", assembly);
4:
5: Type[] foundAssemblyTypes;
6:
7: try
8: {
9: foundAssemblyTypes = assembly.GetTypes();
10: }
11: catch (ReflectionTypeLoadException typeLoadException)
12: {
13: foundAssemblyTypes = (from type in typeLoadException.Types
14: where type != null
15: select type).ToArray();
16:
17: Log.Warning("A ReflectionTypeLoadException occured, adding all {0} types that were loaded correctly", foundAssemblyTypes.Length);
18:
19: if (logLoaderExceptions)
20: {
21: Log.Warning("The following loading exceptions occurred:");
22: foreach (var error in typeLoadException.LoaderExceptions)
23: {
24: Log.Warning(" " + error.Message);
25: }
26: }
27: }
28:
29: return foundAssemblyTypes;
30: }
So, what have we learned today? Even unit tests cannot be trusted…
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