class_docstr: Test the dependency tree.
  
  This is what we are working with::
  
      None (No Data)
       +DataID(name='comp19')
       + +DataID(name='ds5', resolution=250, modifiers=('res_change',))
       + + +DataID(name='ds5', resolution=250, modifiers=())
       + + +__EMPTY_LEAF_SENTINEL__ (No Data)
       + +DataID(name='comp13')
       + + +DataID(name='ds5', resolution=250, modifiers=('res_change',))
       + + + +DataID(name='ds5', resolution=250, modifiers=())
       + + + +__EMPTY_LEAF_SENTINEL__ (No Data)
       + +DataID(name='ds2', resolution=250, calibration=<calibration.reflectance>, modifiers=())
docstr: Set up the test tree.
docstr_tok: ["Set","up","the","test","tree","."]
code: def setUp(self):
      """Set up the test tree."""
      self.dependency_tree = DependencyTree(None, None, None)
  
      composite_1 = make_cid(name="comp19")
      dependency_1 = make_dataid(
          name="ds5", resolution=250, modifiers=("res_change",)
      )
      dependency_1_1 = make_dataid(
          name="ds5", resolution=250, modifiers=tuple()
      )
      node_composite_1 = self.dependency_tree.add_leaf(composite_1)
      node_dependency_1 = self.dependency_tree.add_leaf(
          dependency_1, node_composite_1
      )
      self.dependency_tree.add_leaf(dependency_1_1, node_dependency_1)
      # ToDo: do we really want then empty node to be at the same level as the unmodified data?
      node_dependency_1.add_child(self.dependency_tree.empty_node)
  
      dependency_2 = make_cid(name="comp13")
      dependency_2_1 = dependency_1
      node_dependency_2 = self.dependency_tree.add_leaf(
          dependency_2, node_composite_1
      )
      self.dependency_tree.add_leaf(dependency_2_1, node_dependency_2)
      # We don't need to add the unmodified dependency a second time.
  
      dependency_3 = make_dataid(
          name="ds2",
          resolution=250,
          calibration="reflectance",
          modifiers=tuple(),
      )
      self.dependency_tree.add_leaf(dependency_3, node_composite_1)
  
imports: import os
  import unittest
  from satpy.dependency_tree import DependencyTree
  from satpy.tests.utils import make_cid, make_dataid
label_desc: Use image node_id 1 for calling the TestDependencyTree obj's underlying member method code with example usage: obj.setUp() without return types