Convert multiselect test to Selenium

.gitignore

@@ -27,6 +27,7 @@ __pycache__
 \#*#
 .#*
 .coverage
+.pytest_cache
 src
 
 *.swp
@@ -38,4 +39,5 @@ config.rst
 /.project
 /.pydevproject
 
-package-lock.json
+package-lock.json
+geckodriver.log

notebook/tests/selenium/test_multiselect.py

@@ -0,0 +1,65 @@
+def test_multiselect(notebook):
+    def extend_selection_by(delta):
+        notebook.browser.execute_script(
+            "Jupyter.notebook.extend_selection_by(arguments[0]);", delta)
+
+    def n_selected_cells():
+        return notebook.browser.execute_script(
+            "return Jupyter.notebook.get_selected_cells().length;")
+
+    a = 'print("a")'
+    b = 'print("b")'
+    c = 'print("c")'
+    notebook.edit_cell(index=0, content=a)
+    notebook.append(b, c)
+
+    notebook.focus_cell(0)
+    assert n_selected_cells() == 1
+
+    # Check that only one cell is selected according to CSS classes as well
+    selected_css = notebook.browser.find_elements_by_css_selector(
+        '.cell.jupyter-soft-selected, .cell.selected')
+    assert len(selected_css) == 1
+
+    # Extend the selection down one
+    extend_selection_by(1)
+    assert n_selected_cells() == 2
+
+    # Contract the selection up one
+    extend_selection_by(-1)
+    assert n_selected_cells() == 1
+
+    # Extend the selection up one
+    notebook.focus_cell(1)
+    extend_selection_by(-1)
+    assert n_selected_cells() == 2
+
+    # Convert selected cells to Markdown
+    notebook.browser.execute_script("Jupyter.notebook.cells_to_markdown();")
+    cell_types = notebook.browser.execute_script(
+        "return Jupyter.notebook.get_cells().map(c => c.cell_type)")
+    assert cell_types == ['markdown', 'markdown', 'code']
+    # One cell left selected after conversion
+    assert n_selected_cells() == 1
+
+    # Convert selected cells to raw
+    notebook.focus_cell(1)
+    extend_selection_by(1)
+    assert n_selected_cells() == 2
+    notebook.browser.execute_script("Jupyter.notebook.cells_to_raw();")
+    cell_types = notebook.browser.execute_script(
+        "return Jupyter.notebook.get_cells().map(c => c.cell_type)")
+    assert cell_types == ['markdown', 'raw', 'raw']
+    # One cell left selected after conversion
+    assert n_selected_cells() == 1
+
+    # Convert selected cells to code
+    notebook.focus_cell(0)
+    extend_selection_by(2)
+    assert n_selected_cells() == 3
+    notebook.browser.execute_script("Jupyter.notebook.cells_to_code();")
+    cell_types = notebook.browser.execute_script(
+        "return Jupyter.notebook.get_cells().map(c => c.cell_type)")
+    assert cell_types == ['code'] * 3
+    # One cell left selected after conversion
+    assert n_selected_cells() == 1