4.x: Unit test lambdaification 17 of N

[akarnokd]

IntelliJ -> Inspect lambdas that can be converted to method references ~ 710 instances.

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.583 bits/char
Verdict: ✅ Mid-4 beauty detected (thoughtful human code!)

Changed files entropy:

src/test/java/io/reactivex/rxjava4/flowable/FlowableNullTests.java: 4.908
src/test/java/io/reactivex/rxjava4/flowable/FlowableSubscriberTest.java: 4.437
src/test/java/io/reactivex/rxjava4/internal/observers/CompletableConsumersTest.java: 4.707
src/test/java/io/reactivex/rxjava4/internal/observers/MaybeConsumersTest.java: 4.674
src/test/java/io/reactivex/rxjava4/internal/observers/ObservableConsumersTest.java: 4.670
src/test/java/io/reactivex/rxjava4/internal/observers/SingleConsumersTest.java: 4.714
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableMergeTest.java: 4.587
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableBufferTest.java: 4.685
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableConcatMapEagerTest.java: 4.693
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableConcatMapSchedulerTest.java: 4.752
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableConcatTest.java: 4.665
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableElementAtTest.java: 4.635
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableFlatMapTest.java: 4.639
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableFlattenIterableTest.java: 4.495
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableFromIterableTest.java: 4.397
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableGroupByTest.java: 4.632
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableMaterializeTest.java: 4.653
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableMergeTest.java: 4.644
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableObserveOnTest.java: 4.543
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableReplayEagerTruncateTest.java: 4.740

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.74%. Comparing base (5f3e76b) to head (5fb9cb3).

Additional details and impacted files

@@             Coverage Diff              @@
##                4.x    #8158      +/-   ##
============================================
+ Coverage     98.72%   98.74%   +0.01%     
+ Complexity     6937     6932       -5     
============================================
  Files           773      773              
  Lines         48990    48984       -6     
  Branches       6586     6586              
============================================
+ Hits          48366    48369       +3     
+ Misses          456      453       -3     
+ Partials        168      162       -6     

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