Simplifiy existing split of tests

[wind57]

No description provided.

[wind57]

The easiest way to explain what this is doing is via an example. This piece of code acts as a "function", and each step of the matrix (32 instances) call this function.

As input to it, it provides:

• CURRENT_INDEX (number of the current instance of the matrix), this value is between 0 and 31, inclusiv.

As an output it will provide two things:

• start_from
• how_many

This part is easy to understand via an actual example.

---

Suppose we have such a config: there are a total of 347 tests to be run on 32 instances (matrix steps). We need to split these. If we had 320 tests, the distribution would have been easy:

320 / 32 = 10, so each instance of the matrix would run 10 tests. In that case, let's suppose CURRENT_INDEX = 0, as such:

start_from = 0
how_many = 10

that is, for the case when matrix step = 0 (current_index = 0), we would need to start at the zero index of the entire list of tests and take 10 of them.

If current_index = 1, then start_from = 10 and how_many = 10. If current_index = 2, then start_from=20 and how_many = 10, and so on.

To map current_index to it's actual start_from and how_many, I name them: start_from_${CURRENT_INDEX} and how_many_${CURRENT_INDEX}. For example:

current_index = 0 => `start_from_0 = 0, how_many_0 = 10`
current_index = 1 => `start_from_1 = 10, how_many_1 = 10`
current_index = 2 => `start_from_0 = 20, how_many_0 = 10`

These start_from_0 = 0, how_many_0 = 10 are set as environment variables, so that they could be referenced in the common code later.

---

For a distribution that is not perfect, 347 tests across 32 instances, the idea is simple also:

• first pretend there is a perfect distribution: 347 / 32 = 10
• then compute the reminder : 347 - 347/ 32 = 25

This means we are left with 25 tests that should go to "some" instances. And Ido this like this:

give each first "reminder of instances" (25), each one extra test. In numbers:

current_index = 0 => `start_from_0 = 0, how_many_0 = 10 + 1`
current_index = 1 => `start_from_0 = 11, how_many_0 = 10 + 1`
current_index = 2 => `start_from_0 = 22, how_many_0 = 10 + 1`

...

The rest of instances, that is 26-th, 27-th and so one will each run 10 tests.

I honestly hope this makes sense.

[wind57]

what is the name of the env variable that we need:

start_from_name would be something like start_from_0 or start_from_2 etc. Same for how_many_name.

Once I know the name, I read its value: start_from=${!start_from_name} and how_many=${!how_many_name}

This is later used to "slice" the array of all tests:

sliced_array=(${SORTED_TEST_CLASSNAMES[@]:$start_from:$how_many})

and these are the tests that a certain matrix step runs.

[wind57]

@ryanjbaxter final PR before I can focus on the balanced tests splits. thank you for looking into it