Fix bug in wraplines

A long string without spaces would cause infinite recursion because
the space at the beginning would always be found.

Now the function is tested thoroughly.

src/reportengine/helputils.py

@@ -42,15 +42,20 @@ def _indent():
 
     def wraplines(txt):
         for line in txt.splitlines(keepends=True):
-            line = "%s%s" % (next(indent), line)
+            ni = next(indent)
+            line = f"{ni}{line}"
             if len(line) >= width:
-                break_space = line[:width].rfind(' ')
+                #Break by the last space before the with limit
+                break_space = line.rfind(' ', len(ni), width)
                 if break_space == -1:
-                    yield line
-                else:
-                    yield line[:break_space] + '\n'
-                    #+1 removes the marching space
-                    yield from wraplines(line[break_space+1:])
+                    #If not possible, break by the first space afer the limit
+                    break_space = line.find(' ', width)
+                    if break_space == -1:
+                        yield line
+                        continue
+                yield line[:break_space] + '\n'
+                #+1 removes the marching space
+                yield from wraplines(line[break_space+1:])
             else:
                 yield line
     return list(wraplines(txt))

src/reportengine/tests/test_helputils.py

@@ -0,0 +1,16 @@
+import re
+
+from hypothesis import given
+from hypothesis.strategies import text
+
+from reportengine import helputils
+
+@given(text(min_size=1, max_size=1000))
+def test_sane_wrap(txt):
+    ind = '    '
+    w = 70
+    res = helputils.sane_fill(txt, initial_indent=ind, width=w)
+    assert res.startswith(ind)
+    assert re.sub(r'\s', '', txt) == re.sub(r'\s', '', res)
+    for line in res.splitlines():
+        assert line.rfind(' ') < w