Standardize test src path so unit tests run.

The project has a glitch such that the `test` directory is currently tucked under `main`.  That glitch makes Maven not find it.  This changeset moves the `test` directory under `src` where Maven expects it.

Before:

```
$ mvn test
...
[INFO] No tests to run.
...
```

After:

```
$ mvn test
...
Results :

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0
...
```