Is TEST_EXTENSIONS a user or developer variable?

[Arthur Schwarz]

Win7-64 bits
Cygwin
Automake 1.14,  Nov 2013

15.2.3 Parallel Test Harness
Pg. 113

"TEST_EXTENSIONS defaults to .test; it can be overridden by the user ..."

All examples indicate that this is a developer variable, and the body of
thext seems to focuse on the develop and not the user. Is there a role for
this on the user side? How can it be used?

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