README: add a minimal test for slapos.recipe.build default recipe

README.rst

@@ -48,6 +48,71 @@ Using the init option::
   [section-two]
   bar = ${section-one:foo}
 
+
+A simplified example::
+
+  >>> write(sample_buildout, 'buildout.cfg',
+  ... """
+  ... [buildout]
+  ... parts = section-two
+  ...
+  ... [section-one]
+  ... recipe = slapos.recipe.build
+  ... init =
+  ...   options['foo'] = 'foo from section-one'
+  ...
+  ... [section-two]
+  ... recipe = slapos.recipe.build
+  ... bar = ${section-one:foo}
+  ... install =
+  ...   import os
+  ...   os.mkdir(options['location'])
+  ...   print('Installed section-two with option %s.' % options['bar'])
+  ... """)
+
+  >>> print(system(buildout))
+  Installing section-one.
+  Installing section-two.
+  Installed section-two with option foo from section-one.
+  ...
+
+  >>> ls(sample_buildout, 'parts')
+  d section-two
+
+In case of error, a proper traceback is displayed and nothing is installed
+
+  >>> write(sample_buildout, 'buildout.cfg',
+  ... """
+  ... [buildout]
+  ... parts = section-two
+  ...
+  ... [section-two]
+  ... recipe = slapos.recipe.build
+  ... install =
+  ...   import os
+  ...   os.mkdir(options['location'])
+  ...   print(1 / 0.) # this is an error !
+  ... """)
+
+  >>> print(system(buildout))
+  Uninstalling section-two.
+  Uninstalling section-one.
+  Installing section-two.
+  ...
+  While:
+    Installing section-two.
+  <BLANKLINE>
+  An internal error occurred due to a bug in either zc.buildout or in a
+  recipe being used:
+  Traceback (most recent call last):
+  ...
+    File "<string>", line 3, in <module>
+  ZeroDivisionError: float division by zero
+
+  >>> ls(sample_buildout, 'parts')
+  <BLANKLINE>
+
+
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 ~~~~~~~~~~~~~