Support usage in Jupyter notebooks

Description

When using FluentAssertions in a C# Jupyter notebook and the assertion fails, the exception is not pertaining to the actual mismatch, but regarding missing infrastructure.

Complete minimal example reproducing the issue

Expected behavior:

The expected exception for the above example is:

Expected value to be 99, but found 1.
   at FluentAssertions.Execution.LateBoundTestFramework.Throw(String message)
   at FluentAssertions.Execution.TestFrameworkProvider.Throw(String message)
   at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
   ...

Actual behavior:

The actual exception is:

Unhandled Exception
Could not load file or assembly 'System.Configuration.ConfigurationManager, Version=4.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'. Reference assemblies should not be loaded for execution.  They can only be loaded in the Reflection-only loader context. (0x80131058)
   at FluentAssertions.Common.AppSettingsConfigurationStore.GetSetting(String name)
   at FluentAssertions.Common.Configuration.get_ValueFormatterAssembly() in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Common\Configuration.cs:line 88
   at FluentAssertions.Common.Configuration.DetermineFormatterDetectionMode() in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Common\Configuration.cs:line 55
   at FluentAssertions.Common.Configuration.get_ValueFormatterDetectionMode() in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Common\Configuration.cs:line 40
   at FluentAssertions.Formatting.AttributeBasedFormatter.get_IsScanningEnabled() in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Formatting\AttributeBasedFormatter.cs:line 33
   at FluentAssertions.Formatting.AttributeBasedFormatter.CanHandle(Object value) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Formatting\AttributeBasedFormatter.cs:line 28
   at FluentAssertions.Formatting.Formatter.<>c__DisplayClass7_0.<Format>b__0(IValueFormatter f) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Formatting\Formatter.cs:line 138
   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Func`2 predicate, Boolean& found)
   at System.Linq.Enumerable.First[TSource](IEnumerable`1 source, Func`2 predicate)
   at FluentAssertions.Formatting.Formatter.Format(Object value, FormattingContext context, FormatChild formatChild) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Formatting\Formatter.cs:line 138
   at FluentAssertions.Formatting.Formatter.ToString(Object value, Boolean useLineBreaks) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Formatting\Formatter.cs:line 97
   at FluentAssertions.Execution.MessageBuilder.<FormatArgumentPlaceholders>b__6_0(Object a) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\MessageBuilder.cs:line 91
   at System.Linq.Enumerable.SelectArrayIterator`2.ToArray()
   at FluentAssertions.Execution.MessageBuilder.FormatArgumentPlaceholders(String failureMessage, Object[] failureArgs) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\MessageBuilder.cs:line 91
   at FluentAssertions.Execution.MessageBuilder.Build(String message, Object[] messageArgs, String reason, ContextDataItems contextData, String identifier, String fallbackIdentifier) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\MessageBuilder.cs:line 40
   at FluentAssertions.Execution.AssertionScope.<>c__DisplayClass30_0.<FailWith>b__0() in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\AssertionScope.cs:line 200
   at FluentAssertions.Execution.AssertionScope.FailWith(Func`1 failReasonFunc) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\AssertionScope.cs:line 216
   at FluentAssertions.Execution.AssertionScope.FailWith(Func`1 failReasonFunc) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\AssertionScope.cs:line 196
   at FluentAssertions.Execution.AssertionScope.FailWith(String message, Object[] args) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Execution\AssertionScope.cs:line 238
   at FluentAssertions.Numeric.NumericAssertions`1.Be(T expected, String because, Object[] becauseArgs) in C:\projects\fluentassertions-vf06b\Src\FluentAssertions\Numeric\NumericAssertions.cs:line 51
   at Submission#7.<<Initialize>>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.CodeAnalysis.Scripting.ScriptExecutionState.RunSubmissionsAsync[TResult](ImmutableArray`1 precedingExecutors, Func`2 currentExecutor, StrongBox`1 exceptionHolderOpt, Func`2 catchExceptionOpt, CancellationToken cancellationToken)

The behavior does not change if #r "nuget:System.Configuration.ConfigurationManager" is added to the cell before loading FluentAssertions.

Versions

• Which version of Fluent Assertions are you using? The latest version downloaded by the #r statement.
• Which .NET runtime and version are you targeting? The latest .NET Core version installed into the Jupyter Docker image.

[ralfw]

Thanks for the workaround! I can live with that for now. But a solution to the root problem would be nice, too, of course.😉

[jnyrup]

Yes, I’m good with the decorator approach.