TST: Add test for correct row ordering

Add test to verify summary_col preserved order

closes statsmodels#3767

statsmodels/iolib/tests/test_summary2.py

@@ -56,6 +56,27 @@ def test_summarycol_drop_omitted(self):
         assert 'const' in str(actual)
         assert 'x2' in str(actual)
 
+    def test_summary_col_ordering_preserved(self):
+        # gh-3767
+        x = [1, 5, 7, 3, 5]
+        x = add_constant(x)
+        x2 = np.concatenate([x, np.array([[3], [9], [-1], [4], [0]])], 1)
+        y1 = [6, 4, 2, 7, 4]
+        y2 = [8, 5, 0, 12, 4]
+        reg1 = OLS(y1, x2).fit()
+        reg2 = OLS(y2, x2).fit()
+        info_dict = {'R2': lambda x: '{:.3f}'.format(int(x.rsquared)),
+                     'N': lambda x: '{0:d}'.format(int(x.nobs))}
+        original = actual = summary_col([reg1, reg2], float_format='%0.4f')
+        actual = summary_col([reg1, reg2], regressor_order=['x2', 'x1'],
+                             float_format='%0.4f',
+                             info_dict=info_dict)
+        variables = ('const', 'x1', 'x2')
+        for line in str(original).split('\n'):
+            for variable in variables:
+                if line.startswith(variable):
+                    assert line in str(actual)
+
     def test_OLSsummary(self):
         # Test that latex output of regular OLS output still contains
         # multiple tables