Add module documentation for kotlin.test

libraries/kotlin.test/Module.md

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+# Module kotlin.test
+
+## kotlin.test
+
+kotlin.test provides a set of utility functions for performing assertions in tests, independently of the test framework
+being used. The functions are defined as  [top-level functions in the package](kotlin.test/index.html#functions).
+
+The test framework is abstracted through the [Asserter] class. A basic [Asserter] implementation is provided out of the
+box. The `kotlin-test-junit` module provides an implementation of [Asserter] on top of JUnit. Note that the class is not intended
+to be used directly from tests.