4.x: Unit test lambdaification 19 of N

[akarnokd]

Will go over the unit tests in ASCII order of the classpath and classes.

IntelliJ: Inspect -> RedundantCast, Inspect -> Anonymous type can be replaced by lambda
Search regexp: new\s+\w+(?:\s*<(?:[\s\w<>(\[\])?,.?]|\s*<[\s\w<>(\[\])?,.?]*>)*>)?\s*\([^)]*\)\s*\{

/* NFI */ = Not Functional Interface so break the regexp pattern

If you complain instead of proposing a PR about "why not convert to method references" you'll be banned.

Related: #8080

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.689 bits/char
Verdict: ✅ Mid-4 beauty detected (thoughtful human code!)

Changed files entropy:

src/main/java/io/reactivex/rxjava4/observers/TestObserver.java: 4.608
src/main/java/io/reactivex/rxjava4/subscribers/TestSubscriber.java: 4.601
src/test/java/io/reactivex/rxjava4/internal/observers/DeferredScalarObserverTest.java: 4.428
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableCacheTest.java: 4.595
src/test/java/io/reactivex/rxjava4/internal/operators/flowable/FlowableZipTest.java: 4.765
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeAmbTest.java: 4.605
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeCacheTest.java: 4.683
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeCallbackObserverTest.java: 4.714
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeConcatArrayTest.java: 4.637
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeConcatIterableTest.java: 4.846
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeConcatMapCompletableTest.java: 4.934
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeConcatMapSingleTest.java: 4.762
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeConcatMapTest.java: 4.887
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeCreateTest.java: 4.195
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeDematerializeTest.java: 4.828
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeDoAfterSuccessTest.java: 4.767
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeDoFinallyTest.java: 4.671
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeDoOnEventTest.java: 4.774
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeDoOnTerminateTest.java: 4.759
src/test/java/io/reactivex/rxjava4/internal/operators/maybe/MaybeFlatMapBiSelectorTest.java: 4.781

✅ 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 98.72%. Comparing base (1e4ffe7) to head (25c50b6).

Additional details and impacted files

@@             Coverage Diff              @@
##                4.x    #8161      +/-   ##
============================================
- Coverage     98.77%   98.72%   -0.06%     
+ Complexity     6940     6937       -3     
============================================
  Files           773      773              
  Lines         48994    48994              
  Branches       6586     6586              
============================================
- Hits          48394    48369      -25     
- Misses          439      447       +8     
- Partials        161      178      +17     

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