When running unit tests, install the package itself first.

.travis.yml

@@ -95,7 +95,7 @@ install:
     - pip install -U pip
     - if [[ "${MAIN_CMD}" == pycodestyle ]]; then pip install pycodestyle; fi
     - if [[ "${MAIN_CMD}" == sphinx-build* ]]; then pip install Sphinx; fi
-    - if [[ "${MAIN_CMD}" == pytest ]]; then pip install -r requirements.txt; fi
+    - if [[ "${MAIN_CMD}" == pytest ]]; then pip install -r requirements.txt; pip install . ; fi
     - if [[ "${SETUP_CMD}" == '--cov' ]]; then pip install pytest-cov coveralls; fi
     # - if [[ "${MAIN_CMD}" == python* || "${MAIN_CMD}" == coverage* ]]; then pip install -r requirements.txt; fi
     - if [[ -n "${ASTROPY_VERSION}" ]]; then pip install -U "astropy${ASTROPY_VERSION}"; fi