ESL tests should almost always contain an oral component. You can conduct one in a similar way to an ordinary speaking activity. Arrange the class into groups or pairs and assign a speaking task appropriate to the class's language level. Circulate as the students work, awarding points for both fluency and accuracy.
Evaluate students throughout the course and give them continued feedback so that they have a fairly accurate idea of how they are progressing before they take any test. Some students worry disproportionately about tests and do not perform well, while others whose performance in class may not be particularly impressive, excel. Impress on your students that tests are just one way for you and them to evaluate their progress, not the only way.
Only test students on material you have covered in class. A test should, as accurately as is possible, measure students' progress in class, not their overall English ability. In addition, give a wide variety of different types of questions. A reading test, for example, might include multiple choice and full-answer comprehension questions, vocabulary matching exercises and a skim reading task.
Make sure that all the students understand the rules of the test. Issues that need resolving before a test begins include talking in their native language to other students, using dictionaries, asking the teacher questions and so on. Ask the students questions to determine their understanding rather than just assuming it. You might ask your students, for example, "If you don't understand a question, what should you do?" or, "If you don't understand the meaning of a word in the reading, what are you allowed to do?"