| oEval | Test.IOTasks.Internal.Term, Test.IOTasks.Term |
| oFlush | Test.IOTasks.Internal.Output |
| Opaque | Test.IOTasks.Internal.Term |
| OpenPath | Test.IOTasks.Constraints |
| OptFlag | Test.IOTasks.Trace |
| Optional | Test.IOTasks.Trace |
| Or | Test.IOTasks.Internal.Term |
| ordinaryTrace | Test.IOTasks.Trace |
| Outcome | |
| 1 (Type/Class) | Test.IOTasks.Testing, Test.IOTasks, Test.IOTasks.Random |
| 2 (Data Constructor) | Test.IOTasks.Testing, Test.IOTasks, Test.IOTasks.Random |
| OutcomeHints | Test.IOTasks.Testing, Test.IOTasks, Test.IOTasks.Random |
| OutOfInputs | Test.IOTasks.Trace |
| outOfInputs | Test.IOTasks.Trace |
| Output | Test.IOTasks.Internal.Output |
| OutputPattern | Test.IOTasks.Internal.OutputPattern, Test.IOTasks.OutputPattern, Test.IOTasks, Test.IOTasks.Random |
| Overflow | Test.IOTasks.Constraints |
| OverflowConstraints | Test.IOTasks.Constraints |
| OverflowHint | Test.IOTasks.Testing, Test.IOTasks, Test.IOTasks.Random |
| OverflowOccurred | Test.IOTasks.Internal.Overflow, Test.IOTasks.Overflow |
| OverflowTreatment | |
| 1 (Type/Class) | Test.IOTasks.Internal.Overflow |
| 2 (Data Constructor) | Test.IOTasks.Internal.Overflow |
| OverflowWarning | Test.IOTasks.Internal.Overflow, Test.IOTasks.Overflow |
| overflowWarnings | Test.IOTasks.Testing, Test.IOTasks, Test.IOTasks.Random |