Implement Selective Testing

[aszecowka]

ClusterTestSuite has defined selectors:

• matchNames
• matchLabels

Currently, we run all the tests. Implement running only tests defined by selectors.

[sjanota]

There is a problem with matchNames: TestDefinitions are namespaced, but we don't require namespace in selector. The only solution would be to fetch all namespaces and scan them in a for loop, but that sounds weak to me. I guess we must enhance matchNames with namespace.

There are some places in kubernetes where a convention namespace:name is used. auth can-i is one of those places. Maybe we can stick to it?

[sjanota]

Right now the TestSelector is defined as follows:

type TestsSelector struct {
	// Find test definitions by it's name
	MatchNames []TestDefReference `json:"matchNames,omitempty"`
	// Find test definitions by it's labels.
	// TestDefinition should have AT LEAST one label listed here to be executed.
	MatchLabels []string `json:"matchLabels,omitempty"`
}

The idea was that MatchLabels contains list of label names to match using EXISTS operator.

I suggest we change the approach to something like this:

type TestsSelector struct {
    // Find test definitions by it's name
    MatchNames []TestDefReference `json:"matchNames,omitempty"`
    // Find test definitions by it's labels.
    // TestDefinition should match AT LEAST one expression listed here to be executed.
    // For a complete grammar see: https://github.com/kubernetes/apimachinery/blob/master/pkg/labels/selector.go#L811
    MatchLabelExpressions []string `json:"matchLabels,omitempty"`
} 

Thanks to that we can utilize apimachinery labels.Parse function. The semantics would be OR, so every TD that matches at least one of the listed expressions should be executed.

[sjanota]

I'll go with the idea. PR should appear shortly.