test: remove t aliasing and normalise naming of test cases in subtests

What does this MR do?

This MR cleans up the way we do subtests so that:

• there is no aliasing on t variable in subtests
• the name of the loop item is testCase and not the test and the test is already assigned to the main test running the subtests.

The goal is to make tests more readable - more often than I would like, I had to double-check if t is the root test t or the subtest one. It slows reading tests down. Renaming testcases was necessary as well because in lots of cases the testcase was named tt which was blocking the rename so I standardised it as well.

So, instead of:

       for _, tt := range tests {
               t.Run(tt.name, func(t *testing.T) {

I rewrote all loops to:

       for _, tc := range testCases {
               t.Run(tc.name, func(tt *testing.T) {

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