Rosik/more cas tests

Summary

• test: one more cas unit test

• test: one more case for test_cas_predicate

• test: improve test_cas_predicate

• test: refactor cas unit tests

• chore: reword doc comment on Range::for_op

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• Close nothing
• Follow-up for !1270 (merged)
• Cherry-pick to: none
• Docs follow-up: not necessary