ts: improve replaceFirstInStr proc coverage

Signed-off-by: Xavier Delaruelle <xavier.delaruelle@cea.fr>

Author: xdelaruelle

testsuite/example/siteconfig.tcl-1

@@ -711,4 +711,8 @@ if {[info exists env(TESTSUITE_ENABLE_SITECONFIG_GETVIAMODULEMODULEPATH)]} {
     report [string length [getViaModuleModulepath unk]]
 }
 
+if {[info exists env(TESTSUITE_ENABLE_SITECONFIG_REPLACEFIRSTINSTR)]} {
+    report [replaceFirstInStr string unk foo]
+}
+
 }

testsuite/modules.00-init/120-siteconfig.exp

@@ -829,6 +829,13 @@ lappend ans $vers_reportre
 testouterr_cmd_re sh -V OK [join $ans \n]
 unsetenv_var TESTSUITE_ENABLE_SITECONFIG_GETVIAMODULEMODULEPATH
 
+setenv_var TESTSUITE_ENABLE_SITECONFIG_REPLACEFIRSTINSTR 1
+set ans [list]
+lappend ans string
+lappend ans $vers_reportre
+testouterr_cmd_re sh -V OK [join $ans \n]
+unsetenv_var TESTSUITE_ENABLE_SITECONFIG_REPLACEFIRSTINSTR
+
 } elseif {$verbose} {
     send_user "\tSkip tests relying on an excepted siteconfig file installed\n"
 }