The test current is the minimum current to ensure good regulation. The maximum current represents the maximum safe current that the diode can handle. IF operation at above maximum current will destroy the zener.
munich1806,
Test current is the current at which the zener breakdown voltage and equivalent internal impedance specifications are guaranteed. Currents higher than the test current result in slightly higher breakdown voltage and lower internal impedance. Conversly, currents lower thatn the test current result in slightly lower breakdown voltage and higher internal impedance.
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Maximum current is as stated by wisepie.
Regards,
Kral