The level of proficiency in any foreign language is checked using standardized tests. As a rule, tests consist of several parts, where each is aimed at assessing a certain skill: reading, writing, speaking, or listening. However, there is another approach to measuring the knowledge of foreign language learners, which is being researched and developed as an alternative and more advanced one. This approach focuses only on speech production, i.e. speaking and writing, and it does not test foreign language comprehension, i.e. reading and listening. The approach began to develop when a distinction was made between fluency of speech and the correct use of grammar and syntactic constructions. In English literature, it is called CAF (complexity, accuracy, and fluency). As you can understand, to assess the level of language proficiency, it aims to check these three factors.
Accuracy is considered the simplest factor since it can be determined by the number of errors, which shows the degree of deviation from the normative language.
Fluency shows the general level of language proficiency. It reflects the ability to speak at a normal pace without stammering and doubts when choosing words and structures.
Complexity is the most controversial factor of the three as it is associated with the use of complex structures, the choice of rare and unusual words, and the development of speech in a foreign language in general. At the same time, complexity is defined as a combination of simple structures and words with complex ones.
CAF is still used only in studies of foreign language acquisition. Scientists have not yet come to common terminology and methods for measuring these factors. However, some discoveries can help you in learning a foreign language. For example, it is impossible to improve all the three factors at the same time. It is necessary to choose one, the weakest or the most necessary for you. If it is more important for you to speak quickly at the moment, then you will have to put up with the presence of errors in speech, since the automation of grammar rules takes time and attention. If correct speech is needed more, then the speed will likely be lower but will increase gradually as the correct grammatical forms and constructions are memorized. Focus on one factor that you would like to improve and your progress will be more effective. Have you ever thought about learning a foreign language from this point of view?