Added SpecFlow support

[bjorkstromm]

Added support for SpecFlow. Solves issue #695

At first I thought it would be nice if SpecFlow tool could intercept the Unit Test runner (NUnit/MSTest) just like OpenCover/DotCover, but SpecFlow sets some requirements on the arguments for the Unit Test runner. So it might be simpler to leave it as is.

Unit Tests still to be written.

[patriksvensson]

@mholo65 I see.

Couldn't you use an interceptor but have different settings classes? You could then let the settings classes like NUnitSpecFlowSettings/XUnitSpecFlowSettings (which all derive from SpecFlowSettings) validate and render the arguments for the SpecFlow tool runner.

[bjorkstromm]

@patriksvensson That could actually work.

By intercepting the tool, there shouldn't be any need for separate MSBuild/NUnit/XUnit aliases nor separate Settings classes, one alias for Test Execution reports should be enough.

Example:

public static void SpecFlowExecutionReport(
       Action<ICakeContext> action,
       FilePath projectFile,
       SpecFlowSettings settings
)

The SpecFlow runner should intercept the action (accepting only NUnit/MSTest/XUnit), examine the arguments (and throw exception/try to fix if invalid) and set SpecFlow parameters accordingly.

We'll still need an separate alias for the Step Definition Report though.

[patriksvensson]

@mholo65 Sounds good to me. Implementing the step definition report should probably be done in a separate PR though?

[bjorkstromm]

@patriksvensson could be a separate PR. altough I've implemented it already in this PR :)

[patriksvensson]

@mholo65 Ah, but then proceed as normal 😄

[bjorkstromm]

@patriksvensson that should be it! Could You have a look? When ok, I'll rebase.

[patriksvensson]

@mholo65 Sure, I'll take a look later tonight.

[patriksvensson]

Is this correct?

[patriksvensson]

@mholo65 Left some minor comments, but other than that it looks good to me.

@devlead @gep13 Any other comments about this one?

[bjorkstromm]

@patriksvensson SpecFlow is able to parse test results from either MSTest or NUnit (v2), thus making it compatible with xUnit if the runner is configured to write output in NUnit (v2) format. See #729

The three if-statements could be moved to a separate internal class to enhance readability/maintainability. I will do this + add code examples to documentation for aliases.

Any other comments from @devlead or @gep13?

[bjorkstromm]

@patriksvensson Rebased and moved the argument generation based on Unit Test provider to a separate class.

[devlead]

LGTM 👍 I'll do some local testing and then merge if those go ok.