False positive for empty_xctest_method when assigning statements to _

[mildm8nnered]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Describe the bug

I'm getting a false positive for empty_xctest_method with code like the following:

    func testStuff() {
        _ = 4 + 4
    }

and

    func testStuff() {
        _ = 4 + 4
        _ = 4 + 4
    }

But not

    func testStuff() {
        let aaa = 4 + 4
    }

or

    func testStuff() {
        _ = 4 + 4
        let aaa = 4 + 4
    }

When these methods are members of a subclass of XCTestCase

Sample input:

import XCTest

class MyTests: XCTestCase {
    func testStuff() {
        _ = 4 + 4
    }
}

Complete output when running SwiftLint, including the stack trace and command used

$ swiftlint lint --config swiftlint.yml  t.swift

Linting Swift files at paths t.swift
Linting 't.swift' (1/1)
/tmp/t.swift:4:5: warning: Empty XCTest Method Violation: Empty XCTest method should be avoided. (empty_xctest_method)
Done linting! Found 1 violation, 0 serious in 1 file.

Environment

• SwiftLint version - 0.43.1
• Installation method used - HomeBrew
• Paste your configuration file:

opt_in_rules:
  - empty_xctest_method

• Are you using nested configurations?

No

• Which Xcode version are you using (check xcodebuild -version)?

Xcode 12.4
Build version 12D4e

• Do you have a sample that shows the issue?

import XCTest

class MyTests: XCTestCase {
    func testStuff() {
        _ = 4 + 4
    }
}

[KaneCheshire]

I reported a similar (but different) issue with this rule here too a couple of months ago: #3647

[KaneCheshire]

This looks like an issue with SourceKitten so I've opened an issue there and referenced this issue plus my other issue