feat: adding mfv_existfile.sas and tests

tests/viya/mfv_existfile.test.sas

@@ -0,0 +1,34 @@
+/**
+  @file
+  @brief Testing mfv_existfile macro function
+
+  <h4> SAS Macros </h4>
+  @li mf_uid.sas
+  @li mfv_existfile.sas
+  @li mp_assert.sas
+  @li mv_createfile.sas
+
+**/
+
+options mprint sgen;
+
+%let file=%mf_uid();
+
+/* create a folder */
+filename somefile temp;
+data _null_;
+  file somefile;
+  put 'hello testings';
+run;
+%mv_createfile(path=&mcTestAppLoc/temp, name=&file..txt,inref=somefile)
+
+
+%mp_assert(
+  iftrue=(%mfv_existfile(&mcTestAppLoc/temp/&file..txt)=1),
+  desc=Check if created file exists
+)
+
+%mp_assert(
+  iftrue=(%mfv_existfile(&mcTestAppLoc/temp/%mf_uid().txt)=0),
+  desc=Check if non created file does not exist
+)