discovered here

there seems to be a problem with connection (even across separate installations) during unit tests.
line in common is : line 616 of /lib/simpletestlib/test_case.php: call to UnitTestCaseUsingDatabase->__construct()

pg:
"Debug info:
Warning: pg_connect(): Unable to connect to PostgreSQL server: FATAL: sorry, too many clients already in /home/aparup/mcode/integration/lib/dml/pgsql_native_moodle_database.php on line 164
Stack trace:
line 175 of /lib/dml/pgsql_native_moodle_database.php: dml_connection_exception thrown
line 659 of /admin/tool/unittest/simpletestlib.php: call to pgsql_native_moodle_database->connect()
line 616 of /lib/simpletestlib/test_case.php: call to UnitTestCaseUsingDatabase->__construct()
line 620 of /lib/simpletestlib/test_case.php: call to TestSuite->run()
line 53 of /admin/tool/unittest/ex_simple_test.php: call to TestSuite->run()
line 142 of /admin/tool/unittest/simpletestcoveragelib.php: call to AutoGroupTest->run()
line 119 of /admin/tool/unittest/index.php: call to autogroup_test_coverage->run()
"

ora:
"Debug info: ORA-12516: TNS:listener could not find available handler with matching protocol stack
Stack trace:
line 209 of \lib\dml\oci_native_moodle_database.php: dml_connection_exception thrown
line 659 of \admin\tool\unittest\simpletestlib.php: call to oci_native_moodle_database->connect()
line 616 of \lib\simpletestlib\test_case.php: call to UnitTestCaseUsingDatabase->__construct()
line 620 of \lib\simpletestlib\test_case.php: call to TestSuite->run()
line 53 of \admin\tool\unittest\ex_simple_test.php: call to TestSuite->run()
line 142 of \admin\tool\unittest\simpletestcoveragelib.php: call to AutoGroupTest->run()
line 119 of \admin\tool\unittest\index.php: call to autogroup_test_coverage->run()
"