[SPARK-25249][CORE][TEST]add a unit test for OpenHashMap

[10110346]

What changes were proposed in this pull request?

This PR adds a unit test for OpenHashMap , this can help developers to distinguish between the 0/0.0/0L and null

How was this patch tested?

[maropu]

What do these tests mean? Tests for different type comparisons? e.g.,

    assert(!Some(specializedMap1("a")).contains(0.0))
    assert(!Some(specializedMap1("b")).contains(0.toShort))

[10110346]

if the data type is in @specialized annotation , and the key is not be contained ,the map(key) will return 0
if the data type is not in @specialized annotation , and the key is not be contained ,the map(key) will return null

[maropu]

ah, I see. So, can you describe more in the description?

[10110346]

ok , i will add it

[maropu]

plz add [CORE] in the title?

[10110346]

thanks @maropu

[SparkQA]

Test build #95282 has finished for PR 22241 at commit 76b9f48.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #95285 has finished for PR 22241 at commit 8aea12e.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[kiszk]

Adding tests looks good.
Probably beyond the purpose of this PR, is the following difference intentionally designed?

    // If the data type is in @specialized annotation, and
    // the `key` is not be contained, the `map(key)` will return 0

    // If the data type is not in @specialized annotation, and
    // the `key` is not be contained, the `map(key)` will return null

[srowen]

@kiszk I guess it's because in this case the underlying value type is a primitive like int or long, so null can't be returned?

[srowen]

Merged to master

[SparkQA]

Test build #95286 has finished for PR 22241 at commit 9346112.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.