More tests for different cases are needed, I guess. At least for Python. Sometimes Kata allows me to submit a wrong solution, sometimes - not

Nice kata, but could have been worded more clearly.

Uses exact equality on floats.

See the quotes in your answer, the expected value is a number.

which is obviously incorrect, isn't it?

Got this result expected '5.65' to equal 5.65

Approved

python new test framework is required. updated in this fork

This kata is a subject to deduplication process here: https://github.com/codewars/content-issues/issues/203.
Please join the discussion to help us identify duplicate kata and retire them.

C Translation (author inactive).

All border cases should be tested, 2, 4, 8 and 10 litres in fixed tests in all languages.

Not a kata issue, one of your conditions is wrong:

Purchases of 2 or more litres get a discount of 5 cents per litre

You're doing a 50 cents discount. And because border cases aren't tested your code passed.

Nothing is broken, your switch conditions are wrong:

Purchases of 2 or more litres get a discount of 5 cents per litre...

so I know im getting the discount correct

No, you're not, see the second sample test, print discount value.