Testing people for coronavirus is a key part of the government's plan to tackle the pandemic.
Prime Minister Boris Johnson has set a target of 200,000 tests a day for coronavirus in the UK by the end of May.
Testing is discussed a lot when people talk about coronavirus and experts have criticised the UK's approach so far - they say much more testing needs to be done to work out the scale of the infection in the country and to help us all on the journey back to normal life.
So what is testing? Why is everyone talking about it? And what are the different types?
In the UK, to find out if someone currently has Covid-19, a swab - using a special cotton bud - is taken of their nose or throat and this sample sent off to a lab to look for signs of the virus.
These tests are available to anyone in the UK who is over five and has symptoms.
The testing looks for signs that someone currently has the virus but there is another kind.
It's called an antibody test - and it looks for signs of immunity in the blood and could show whether someone's already had coronavirus.
Antibody tests use a drop of blood which gets placed in an electronic device to see if those specific, coronavirus antibodies, which fought the virus in the body, are present.
After lots of research and trials by scientists all over the world, on 14 May, Public Health England - the government's advisor on all things health and safety - said it has approved a reliable antibody testing kit to see whether people have had coronavirus in the past.
It says the testing kit, developed by a pharmaceutical company in Switzerland, is a "very positive development" in the fight against the virus. The government is now in talks to see if enough of the tests can be made in an affordable way.
Testing can help the government try to track how many cases of the virus there are.
That's important because it means they can monitor the virus, compare it to other countries, and assess how much action they might need to take.
It's also really important for key workers. At the moment, some key workers like doctors, nurses and teachers are having to self-isolate if they've had mild symptoms of the virus. If they did a test which came back negative - it means they could go back to work.
Without testing more widely many people might be self-isolating for no good reason.
The antibody test would tell someone if they have already had coronavirus which might mean that they have immunity, although that is something experts aren't sure of yet and scientists are looking into.
People can gets tests by visiting a testing site or asking for a home-testing kit.
The UK government says it has been working to "ramp up" how many tests it can do - it aimed to be able to do 100,000 a day by the end of April and the target is now 200,000 a day by the end of May.
However, it has not hit its April target on some days, and people have complained that they have not been able to get tests.
The situation has been different in some countries, leading to criticism of the UK government.
Testing depends not just on the number of testing kits, it also depends on the number of laboratories available, how many machines they have and quantities of chemicals needed for the kits to be analysed. These components are in high demand all over the world.
Countries such as South Korea and Germany have had fewer cases of coronavirus than the UK and a big reason given for this is that they both tested far more widely than the UK has.
Both also acted very quickly when the virus was first spreading to stockpile kits and make more labs available for testing.
Some countries also had lots of testing equipment before the pandemic, and unlike them, the UK wasn't able to start mass testing straight away.