Support temporal assertions regarding intersection of a time period and a given datetime

[Seddryck]

It should be possible to assert that a result-set, with a time period, is including/leading/lagging a given datetime. A time period is defined as the closed-open time interval between two datetime.

For lags and leads, it's possible to define a variant immediately="true" to specify that the time-period should starts/ends at the given date.

<system-under-test>
  <result-set>
    ...
  </result-set>
</system-under-test>
<assert>
  <leads timestamp="...">
    <time-period start="#3" end="EndPeriodColumn"/>
    <group-by>...<group-by>
  </leads >
</assert>

The optional group-by let you define that system-under-test rows should not be tested as a single set of rows but should be subdivided into subsets, each subset being defined by the group-by.