Here is the correct syntax for your program:
Proc univariate data = test;
Var variable1;
Histogram;
run;
Note you don't use equals signs in the VAR statement. Now run this program and check your SAS log. Is it error-free? Check for any output. If you are getting text output but not graphic output it is possible that your ODS settings are not correct. Try adding this to your program:
ods HTML;
Proc univariate data = test;
Var variable1;
Histogram;
run;
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