substring_test "iNG", "NG"
=> false

should be
=> true

initials('Barack hussein obama')
=> "B.H.obama"

should be "B.H.Obama"

Something wrong with Ruby random test cases.
In Description: (To be clear, the acceptable characters for the plumage are 8,W,T,Y,U,I,O,A,H,X,V and M.)

Random Tests, Handles a few test cases:
Expected: "HETIHVCZPLIVLWDNDXLMTK8ULIBWYXYYJRIHM8FPTHZIYKATTVVAUOVWWQVJHZVWOQXHS8IRYUZXWMSOYPWJBCTANRUJYHDATFQTRVUNHHDQMFINJZWMICRL''0v0''LRCIMWZJNIFMQDHHNUVRTQFTADHYJURNATCBJWPYOSMWXZUYRI8SHXQOWVZHJVQWWVOUAVVTTAKYIZHTPF8MHIRJYYXYWBILU8KTMLXDNDWLVILPZCVHITEH", instead got: "HTIHVIVWXMT8UIWYXYYIHM8THIYATTVVAUOVWWVHVWOXH8IYUXWMOYWTAUYHATTVUHHMIWMI''0v0''IMWIMHHUVTTAHYUATWYOMWXUYI8HXOWVHVWWVOUAVVTTAYIHT8MHIYYXYWIU8TMXWVIVHITH"

From description: "You need to design a recursive function...."

dropzone([5, 2], [[8, 0], [5, 4], [5, 0]])
Expected: [5, 0], instead got: [5, 4].

Typo in "Find exapmles below:"

table_game [[1,2,1], [1,2,1], [98,99,1]]
=> [1, 1, 98, 1]

wrong

Maybe add a test for [1,1,-1,-1, ... random !=0 ...] (Ruby)?
Several solutions should fail.

arr = [2, 2, -2, -2]
=> [2, 2, -2, -2]
closest arr
=> 2
"Return None if it is not possible to define only one of such values."

arr = [-1, 1]
=> [-1, 1]
explode arr
=> "Void!"

arr = ['-1', 1]
=> ["-1", 1]
explode arr
=> "Void!"

:)

Maybe add a test for ['-2', 2]?

Need a test with two different elements, but the sum of these elements must be equal.
For example,

a = [5] * 10
=> [5, 5, 5, 5, 5, 5, 5, 5, 5, 5]
b = [5] * 10
=> [5, 5, 5, 5, 5, 5, 5, 5, 5, 5]
b[0] -= 2
=> 3
b[1] += 2
=> 7
a
=> [5, 5, 5, 5, 5, 5, 5, 5, 5, 5]
b
=> [3, 7, 5, 5, 5, 5, 5, 5, 5, 5]
a.sum
=> 50
b.sum
=> 50
a[0]+a[1]
=> 10
b[0]+b[1]
=> 10

Several solutions in Ruby:

are_similar a, b
=> true

Please add test with unequal arrays, where a.sum == b.sum (Ruby).
a, b = [1,4,1], [1,3,2]

a, b = [1,4,1], [1,3,2]
are_similar a, b
=> true

Please, add test case for distance = 0 (ruby)