Replace allure-xunit's custom attributes with runner reporter (fixes #344)

[delatrie]

This is the first piece of work to improve allure-xunit out-of-box experience. The main goal here is to drop the [AllureXunit] and [AllureXunitTheory] attributes in favor of the built-in ones: [Fact] and [Theory].

Context

Basically, to generate a report we need to listen for xunit's execution events and extract data provided by xunit in event messages. There are a couple of ways to achieve this.

Previous implementation

Custom attributes ([AllureXunit] and [AllureXunitTheory]) were used to discover tests via the AllureXunitDiscover creating an instance of AllureXunitTestCase for each and injecting the event listener (namely, AllureMessageBus) to handle the events.

The disadvantage is that in order to use allure-xunit one has to modify their test code first replacing built-in xunit attributes with custom ones.

New implementation

We drop the currently implemented extension mechanism in favor of a custom runner reporter (AllureRunnerReporter) that may be used by xunit to directly create an event handler (in our case, an instance of AllureMessageSink) allowing us to bypass the need of custom attributes.

The [AllureXunit] and [AllureXunitTheory] attributes are marked as obsoleted.

Usage

Just install the package and run the tests as usual.

In some cases, allure reporter may not run automatically. In that case, enable the reporter explicitly:

• For VS runner (in Visual Studio, or via the dotnet CLI) use RunConfiguration.ReporterSwitch=allure runsettings option.
• For console runner use -noautoreporters -allure CLI arguments (make sure Allure.XUnit.dll and xunit.console.exe are in the same directory).
• For MSBuild runner speficy the NoAutoReporters="true" Reporter="allure" properties in your xunit task definition (make sure Allure.XUnit.dll and xunit.runner.msbuild.net452.dll are in the same directory).

Additional changes

The PR also adds support for static test methods:

using Xunit;

public class MyTestClass
{
    [Fact]
    public static void StaticMethod()
    {
        Assert.Equal(3, 1 + 2);
    }
}

Previously, such a method caused a test run to be aborted.

Known issues

One reporter per test run

Xunit allows only one active runner reporter. Currently it's impossible to produce allure output files AND, say, send the output to TeamCity at the same test run.

Runners are quite composable though. It should not be that hard to wrap 3rd party's event listener in our own. Support for that will be added in near future.

Arguments of some theories might potentially be unreported

Xunit doesn't provide test arguments to event listeners if one the following conditions is true:

1. A user explicitly disabled theory data pre-enumeration during discovery phase (either on per-test basis or globally).
2. Xunit can't serialize one of a test's argument.

In that case xunit creates one ITestCase instance with null TestMethodArguments property, and multiple ITest instances, one per each argument set. There is no public API allowing to get these arguments.

The PR workarounds this problem by attaching a hook to the XunitTestRunner's constructor at runtime using Harmony. Harmony has its own limitations, the most concerning of which is the inability of Harmony to patch an inlined method. If the constructor of XunitTestRunner is inlined, the patch doesn't work, and arguments of a test that falls into one of the categories above are not reported by allure-xunit. The warning is issued in such a case advising to switch to debug mode.

Checklist

• Sign Allure CLA
• Provide unit tests

[neparij]

Add README notes.
Create issues from Known issues section

[neparij]

Should be either [Obsolete] with for-removal either we should have migration notice

[delatrie]

I've moved the code related to allure model manipulation back to AllureXunitHelper to simplify AllureMessageSink a little. Public methods are refactored and marked as [Obsolete].

[delatrie]

Add README notes.
Create issues from Known issues section

Done!
See #368 and #369 and the updated readme.

[neparij]

AllureLifecycle is a part of Allure.Net.Commons.

[NikitaEgorov]

This PR has broken Rider support completely

https://youtrack.jetbrains.com/issue/RSRP-488382/Load-custom-reporter-dll