The B1 English test is one of the tests created by the CEFR or Common European Framework of Reference for Languages and the UK government uses it as one of the requirements that everyone applying to become a UK citizen need to pass. They can book the test provided either by the Trinity College London or Life Skills Test, as determined by the CEFR. They can book the test on websites such as the one on britishlifeskills.com.
Instead of being a special test, the CEFR is a collection of ‘can do’ statements that list functions you will be able to use in a foreign language at any given skill level. For instance, one of the statements od the ‘can perform’ at the B1 level is “Can create simple and related texts on a general topic or personal interests.” Any foreign language teacher can use this ‘do-able statement’ to evaluate your skills and design lessons to overcome your knowledge gap.