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Each of the build modules in OpenJFX has an addExports file that is imported using @argfile into the test invocation. The addExports file contains entries that export packages that are not public so that the unit tests in the unnamed module can see them. Here is an excerpt from one of the files:
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-XaddExports:
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javafx.base/com.sun.javafx.collections=ALL-UNNAMED
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-XaddExports:
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javafx.
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base/com.sun.javafx.
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property=ALL-UNNAMED
-XaddExports:javafx.base/com.sun.javafx=ALL-UNNAMED
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-XaddExports:
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javafx.
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base/com.sun.javafx.
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event=ALL-UNNAMED
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And example error, that indicates a missing export:
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