I'm using the Product object and store the product sku within the StockKeepingUnit field.
According to the [Winter 18 release notes][1], this field is considered unique, which is totally fine and expected for me.

However, when I use apex testing classes, my product2 testing records that I create for testing are conflicting with the product2 records already part of my Salesforce instance. This doesn't make a lot of sense to me because I am **not** using `seeAllData=true` in my testing classes, those records in my Salesforce instance should not get into conflict with my testing records.

Here is the error message I get when I try to insert a test record that has a product sku equal to a product2 record already part of my Salesforce instance.
`System.DmlException: Insert failed. First exception on row 0; first error: DUPLICATE_VALUE, A Product with this SKU already exists.: [StockKeepingUnit]`

I've tested it in a brand new scratch org to the same result.

**HOW TO REPRODUCE:**

I've added a new product2 record through the dev console
```
Product2 testExistingProduct = new Product2(StockKeepingUnit='60235280574',Name='Fake Name',IsActive=true);
insert testExistingProduct;
```

Here is the testing class

```
@isTest
private class TestDuplicateSku {
    @testSetup static void setup() {
        Product2 testExistingProduct = new Product2(StockKeepingUnit='60235280574',Name='Fake Name',IsActive=true);
        insert testExistingProduct;
    }
    
    @isTest static void   TestBasicProductAddProperties() {
        Test.startTest();
        Test.stopTest();
        Product2 updatedProduct = [select id,StockKeepingUnit from Product2 where StockKeepingUnit='60235280574'];
        System.assertEquals('60235280574',updatedProduct.StockKeepingUnit,
        'Product sku should be defined');
    }
}
```

Error message:
```
TestDuplicateSku.TestBasicProductAddProperties  System.DmlException: Insert failed. First exception on row 0; first error: DUPLICATE_VALUE, A Product with this SKU already exists.: [StockKeepingUnit]

force-app/main/default/classes/TestDuplicateSku.cls:5:1
```

  [1]: https://releasenotes.docs.salesforce.com/en-us/winter18/release-notes/rn_field_service_sku.htm