Doesn't this mean that I cannot give my free consent and am, in fact being coerced into giving consent?
I do not know about the law in South Africa, but under EU law: Yes, this would be interpreted as you being coerced into giving consent.
This follows from the GDPR Receital 43. Here is the relevant part:
Consent is presumed not to be freely given if [...] if the performance of a contract, including the provision of a service, is dependent on the consent despite such consent not being necessary for such performance.
Here "necessary" specifically means "necessary for performing the service" not "necessary for the commercial purposes of the controller".
In your case, the tests are not in any way necessary for providing you with insurance. The only reasons for the tests is to protect the commercial interests of the company. Presumably, if you consent to the tests, and they show that providing you with full coverage would be a financial risk for the company, you will be denied full coverage.
I.e.: Given the GDRP definition of freely given consent, it pretty obvious that this description of your rights:
Your rights are [...]
To refuse to take the test. If you do this you application will be denied.
invalidates any pretense of consent being freely given.
The premise that lies at the root of this question is a very interesting one, that AFAIK is handled different in different jurisdictions.
In the country I live, the majority think that it is politically desirable that all citizens have full coverage, pay the same, and that pre-existing conditions should not exclude anyone from full coverage. This means that insurance companies cannot use the refusal to undergo tests, or refusal to fill in self-declaration questionnaires as grounds to deny someone full coverage, or to charge higher premiums. (In other countries, such as the USA, the majority view is different).
Notice: The GDPR only apply in Europe. If the definition of "freely given consent" is South Africa is different, this may be of no practical use to you.