Ad suggested test unit for "JDK-8234959 FXMLLoader does not populate ENGINE_SCOPE Bindings with FILENAME and ARGV"

[Rony G. Flatscher]

For creating a test unit to test whether [1] is present or not, it is necessary to have a Java
script engine to test again. As discussed in a different thread it is not advisable to use any
concrete, existing Java script engine that is not part of the JDK. Therefore it becomes necessary to
come up with a proper implementation of javax.script.ScriptEngine and
javax.script.ScriptEngineFactory to serve for the sole purpose of testing.

I have come up with such a "pseudo script engine" which will log each script invocation together
with the script code, a copy of the ScriptContext in effect (for later inspection) and the time of
invocation.

For a test unit it is necessary to have this pseudo script engine loaded via the SPI to be able to
use from a test application. For this one can define a
"META-INF/services/javax.script.ScriptEngineFactory" file and/or a "module-info.java" file. In order
to be as flexible as possible both approaches were chosen (also in mind that others may have a need
for such a pseudo script engine for testing purposes). This implementation creates a module that
contains a test application where the ideas and structures are modelled after the "systemTests"
modules (many thanks to Keving Rushforts for pointing at that!).

The test application will create a JavaFX application that processes some fxml file "demo_01.fxml"
which defines the pseudo script engine to be used for executing all of the scripts defined in that
file. The "start" method will fire the Button using  "btn.fire()", "btn.fireEvent( new ActionEvent()
)", and "btn.fireEvent( new MouseEvent( ... ) )" to have the event scripts executed. As mentioned
the pseudo script engine will log each invocation.

Upon return of the "start" method the test application's main method will fetch the log of
invocations from the pseudo script engine and then assert that the sequence of invocations, the
scripts and the ScriptContext Bindings are correct with respect to some "demo_01.fxml". This not
only asserts the proper existence of the entries "javax.script.filename" (also the proper values of
the file names) and "javax.script.argv" in the engine Bindings, but also whether the global Bindings
are correctly defined and their values (and types) are correct. These assertion tests are dependent
on a) how FXMLLoader populates the ScriptContext Bindings and b) how the test case in form of the
fxml-file and the supplied pseudo scripts is formulated.

The test unit uses assertion methods of its own (like the other module based tests) and if it ends
with an exit code of 0 it has passed. In the case of assertion errors (or unexpected errors) an
appropriate error message with a stack trace is given and a non-zero exit code is returned via
"System.exit()" (again modeled after/copied from the other module tests).

To make this test unit as simple as possible the module includes the pseudo script engine (it is not
a separate module). It needs to be run on its own JVM (as is the case with the other module tests).

Any comments, questions, suggestions?

---rony

[1] "JDK-8234959 FXMLLoader does not populate ENGINE_SCOPE Bindings with FILENAME and ARGV":
<https://bugs.openjdk.java.net/browse/JI-9062887>