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https://issues.apache.org/jira/browse/DRILL-5842?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16225780#comment-16225780
]
ASF GitHub Bot commented on DRILL-5842:
---------------------------------------
Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/978#discussion_r147842797
--- Diff:
exec/java-exec/src/test/java/org/apache/drill/exec/physical/unit/MiniPlanUnitTestBase.java
---
@@ -360,7 +366,7 @@ public T columnsToRead(String ... columnsToRead) {
*/
public class JsonScanBuilder extends ScanPopBuider<JsonScanBuilder> {
List<String> jsonBatches = null;
- List<String> inputPaths = Collections.EMPTY_LIST;
+ List<String> inputPaths = Collections.emptyList();
--- End diff --
This is a subtle point. Using the constant creates the expression:
```
public static final List EMPTY_LIST = new EmptyList<>(); // Definition
List<String> inputPaths = EMPTY_LIST; // Original code
```
The above is not type-friendly: we are setting a typed list (`inputPaths`)
to an untyped constant (`EMPTY_LIST`).
The revised code uses Java's parameterized methods to work around the type
ambiguity:
```
public static final <T> List<T> emptyList() ... // Definition
List<String> inputPaths = Collections.emptyList(); // Type-safe assignment
```
Functionally, the two expressions are identical. But, the original was
type-unsafe and generated a compiler warning. The new one is type-safe and
resolves the warning.
> Refactor and simplify the fragment, operator contexts for testing
> -----------------------------------------------------------------
>
> Key: DRILL-5842
> URL: https://issues.apache.org/jira/browse/DRILL-5842
> Project: Apache Drill
> Issue Type: Improvement
> Affects Versions: 1.12.0
> Reporter: Paul Rogers
> Assignee: Paul Rogers
> Fix For: 1.12.0
>
>
> Drill's execution engine has a "fragment context" that provides state for a
> fragment as a whole, and an "operator context" which provides state for a
> single operator. Historically, these have both been concrete classes that
> make generous references to the Drillbit context, and hence need a full Drill
> server in order to operate.
> Drill has historically made extensive use of system-level testing: build the
> entire server and fire queries at it to test each component. Over time, we
> are augmenting that approach with unit tests: the ability to test each
> operator (or parts of an operator) in isolation.
> Since each operator requires access to both the operator and fragment
> context, the fact that the contexts depend on the overall server creates a
> large barrier to unit testing. An earlier checkin started down the path of
> defining the contexts as interfaces that can have different run-time and
> test-time implementations to enable testing.
> This ticket asks to refactor those interfaces: simplifying the operator
> context and introducing an interface for the fragment context. New code will
> use these new interfaces, while older code continues to use the concrete
> implementations. Over time, as operators are enhanced, they can be modified
> to allow unit-level testing.
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