Increase unit test code coverage (now 21%)

test/phpunit/AdherentTest.php

test/phpunit/BuildDocTest.php

test/phpunit/CMailFileTest.php

test/phpunit/CategorieTest.php

test/phpunit/ChargeSocialesTest.php

test/phpunit/CommandeFournisseurTest.php

test/phpunit/CommandeTest.php

test/phpunit/CommonObjectTest.php

test/phpunit/CompanyBankAccountTest.php

test/phpunit/ContratTest.php

test/phpunit/DateLibTest.php

test/phpunit/FactureFournisseurTest.php

test/phpunit/FactureTest.php

test/phpunit/ModulesTest.php

test/phpunit/MyTestSuite.php

test/phpunit/PropalTest.php

test/phpunit/SocieteTest.php

test/phpunit/UserGroupTest.php

test/phpunit/UserTest.php

test/phpunit/phpunittest.xml