Testcase for CBN copy and paste

Testcase for simple CBN copy and paste.
Simulates the following workflow:
1. Create CBN1 [a=10]
2. Run
3. copy and paste CBN1
4. Run
5. Verify that both CBN preview values = 10

@Benglin @lukechurch 
I'd much rather have numeric based comparison instead of ```string```, because for whatever reason if ```mirrorData.Data``` turns out to be a real string, then the validation would have passed (when it should fail obviously). That makes me wonder if the following tweak is possible:

```cs
int expectedValue = 10;
string codeInCBN = "a = " + value;

// Do your thing...

// Validate result...
Assert.AreEqual(mirrorData.Data, value);
```