quickExample fix #201 and pytest

adding testfolder optional input to quickExample() so it can be used in the pytest, and also returning analysis so it can be used in the pytest. Also calls now the interative directory from main.py instead of re-defining it inside.
Solves #201

Added pytest

bifacial_radiance/main.py

@@ -3666,23 +3666,17 @@ def runJob(daydate):
                                      rowWanted=rowWanted,
                                      sensorsy=sensorsy)
 
-def quickExample():
+def quickExample(testfolder=None):
     """
     Example of how to run a Radiance routine for a simple rooftop bifacial system
 
     """
-    def _interactive_directory(title=None):
-        # Tkinter directory picker.  Now Py3.6 compliant!
-        import tkinter
-        from tkinter import filedialog
-        root = tkinter.Tk()
-        root.withdraw() #Start interactive file input
-        root.attributes("-topmost", True) #Bring to front
-        return filedialog.askdirectory(parent=root, title=title)
 
     import bifacial_radiance
-    testfolder = _interactive_directory(title = 'Select or create an empty directory for the Radiance tree')
-    #    testfolder = r'C:\Users\sayala\Documents\RadianceScenes\Demo3'
+
+    if testfolder == None:
+        testfolder = bifacial_radiance.main._interactive_directory(title = 'Select or create an empty directory for the Radiance tree')
+
     demo = bifacial_radiance.RadianceObj('simple_panel',path = testfolder)  # Create a RadianceObj 'object'
 
     #    A=load_inputvariablesfile()
@@ -3723,4 +3717,4 @@ def _interactive_directory(title=None):
     print('Annual bifacial ratio average:  %0.3f' %(
             sum(analysis.Wm2Back) / sum(analysis.Wm2Front) ) )
 
-
+    return analysis

tests/test_bifacial_radiance.py

@@ -30,6 +30,9 @@
 # also test a dummy TMY3 Denver file in /tests/
 MET_FILENAME2 = "724666TYA.CSV"
 
+def test_quickExample():
+    results = bifacial_radiance.main.quickExample(TESTDIR)
+    assert np.mean(results.Wm2Back) == pytest.approx(195380.94444444444, rel = 0.03)  # was 182 in v0.2.2
 
 def test_RadianceObj_set1axis():  
     # test set1axis.  requires metdata for boulder.