Add support for repeated fields in field mask tests

[serhii-lekariev]

This PR addresses #165.

Now assertMatchesMask doesn't skip repeated fields, and instead checks whether at least 1 value is present, and calls a respective assert.

However, repeated fields are only allowed as a last field in the respective mask, so while mask

mask {
    paths: friends
}

can match for a user with friends

message Animal {
    string kind = 1;
}
     
message User {
    string name = 1;
    repeated User friends = 2;
    repeated Animal animals = 3;
}

a mask

mask {
    paths: animals.kind
}

cannot match for any user, because a repeated field is not used as a last one.

[codecov]

Codecov Report

Merging #250 into master will increase coverage by 0.04%.
The diff coverage is 90.9%.

@@             Coverage Diff              @@
##             master     #250      +/-   ##
============================================
+ Coverage     66.38%   66.43%   +0.04%     
- Complexity      583      584       +1     
============================================
  Files           310      310              
  Lines          8158     8167       +9     
  Branches        561      562       +1     
============================================
+ Hits           5416     5426      +10     
+ Misses         2625     2624       -1     
  Partials        117      117

[serhii-lekariev]

@armiol, PTAL.

[armiol]

@serhii-lekariev please see my comments.

[armiol]

This piece of code looks unformatted.

[armiol]

Let's discuss what this test does.

[serhii-lekariev]

@armiol, PTAL.

[serhii-lekariev]

@dmdashenkov, PTAL.

[dmdashenkov]

@serhii-lekariev, please see my comments.

[serhii-lekariev]

@dmdashenkov, PTAL.

[dmdashenkov]

@serhii-lekariev, please fix a few minor comments and LGTM.