Another pass: rough shape of tree and tests

It isn't working yet, the tests don't pass.

But it is on the way!

test/conftest.py

@@ -0,0 +1,22 @@
+import hashlib
+
+import pytest
+
+
+@pytest.fixture
+def leaf():
+    def _leaf(node):
+        return hashlib.sha256(leaf.data).hexdigest()
+
+    return _leaf
+
+
+@pytest.fixture
+def parent():
+    def _parent(left, right):
+        sha256 = hashlib.sha256()
+        sha256.update(left)
+        sha256.update(right)
+        return sha256.hexdigest()
+
+    return _parent

test/test_generator.py

@@ -0,0 +1,66 @@
+"""Generator test module."""
+
+import hashlib
+
+from merkle_tree_stream import MerkleTreeGenerator, MerkleTreeNode
+
+
+def test_hashes(leaf, parent):
+    stream = MerkleTreeGenerator(leaf=leaf, parent=parent)
+
+    stream.next(b'a')
+
+    first_node = (
+        MerkleTreeNode(
+            index=0,
+            parent=1,
+            hash=hashlib.sha256(b'a').hexdigest(),
+            size=1,
+            data=b'a',
+        ),
+    )
+
+    stream.next(b'b')
+
+    second_node = (
+        MerkleTreeNode(
+            index=2,
+            parent=1,
+            hash=hashlib.sha256(b'b').hexdigest(),
+            size=1,
+            data=b'a',
+        ),
+    )
+
+    stream.next(b'c')
+
+    third = hashlib.sha256(b'a')
+    third.update(b'b')
+    third_hash = third.hexdigest()
+
+    third_node = (
+        MerkleTreeNode(index=1, parent=3, hash=third_hash, size=2, data=b'a'),
+    )
+
+    assert stream.nodes == [first_node, second_node, third_node]
+
+
+def test_single_root(leaf, parent):
+    stream = MerkleTreeGenerator(leaf=leaf, parent=parent)
+
+    stream.next('a')
+    stream.next('b')
+    stream.next('c')
+    stream.next('d')
+
+    assert stream.roots.length == 1
+
+
+def multiple_roots(leaf, parent):
+    stream = MerkleTreeGenerator(leaf=leaf, parent=parent)
+
+    stream.next('a')
+    stream.next('b')
+    stream.next('c')
+
+    assert stream.roots.length > 1