[timtebeek]

JUnit's assertInstanceOf returns the cast value, while AssertJ's isInstanceOf returns the assert, so converting a call whose result is used produced code that doesn't compile:

Integer i = assertInstanceOf(Integer.class, o);
// became
Integer i = assertThat(o).isInstanceOf(Integer.class);

The recipe now only converts calls whose result is discarded: a statement in a block, or the body of a lambda whose functional interface returns void (such as assertAll(() -> assertInstanceOf(..)), which keeps converting). Variable initializers, returns, method arguments and value-returning lambdas are left alone. The void check reuses returnsVoid from PlaceAssertJDescriptionBeforeAssertion, now package-private, instead of copying it. The new no-change tests are grouped in a NoChange nested class, and the existing canBeRerun moved there too.

Verified with ./gradlew test --tests 'org.openrewrite.java.testing.assertj.*' --tests 'org.openrewrite.java.testing.testng.TestNgToAssertJTest': 508 tests, 0 failures. No test loads JUnitToAssertj directly; it is covered through the Assertj composite in AssertJBestPracticesTest and TestNgToAssertJTest.

Fixes item D6 of #1211.