diff --git a/day10/day10.py b/day10/day10.py
index 79e0a49..f4b306f 100644
--- a/day10/day10.py
+++ b/day10/day10.py
@@ -35,7 +35,8 @@ def find_s(pipe_map: PipeMap) -> Position:
             return Position(row_idx, col_idx)
         except StopIteration:
             continue
-    raise RuntimeError("No S pipe found!")
+
+    raise AssertionError("No S pipe found!")
 
 
 def calculate_s(start: Position, pipe_map: PipeMap) -> str:
@@ -48,19 +49,22 @@ def calculate_s(start: Position, pipe_map: PipeMap) -> str:
 
     for direction in pipe_directions:
         pos: Position = start.next_position(direction)
-        tile: Pipe | None = pipe_map.get_pipe(pos)
-        if tile is None:
-            raise RuntimeError("Expecting valid pipe")
+        tile: Pipe | None = pipe_map.get_pipe_safe(pos)
+        if tile is None:  # e.g. S is on an edge
+            continue
         opposite_direction = direction.opposite()
         if opposite_direction in Pipe.PIPE_DIRECTION[tile.character]:
             connecting.append(direction)
 
+    if len(connecting) == 0:
+        raise ValueError("S is not a a valid pipe")
+
     # should now have connecting == [NORTH, EAST]:
     for character, pipe_directions in Pipe.PIPE_DIRECTION.items():
         if set(connecting) == set(pipe_directions):
             return character
 
-    raise ValueError("No mapping found for `s` pipe")
+    raise AssertionError("No mapping found for `s` pipe")
 
 
 def find_cycles(pipe_map: PipeMap) -> list[Pipe]:
@@ -210,6 +214,10 @@ def part1(pipe_map: PipeMap) -> int:
 
 def part2(pipe_map: PipeMap) -> int:
     find_cycles(pipe_map)
+
+    # print our map before we mutate it
+    print(pipe_map)
+
     big_map: PipeMap = expand_map(pipe_map)
     # you can use this to view it lol.
     with open("day10/big_unfilled.txt", "w", encoding="utf8") as file:
@@ -227,6 +235,13 @@ def part2(pipe_map: PipeMap) -> int:
         total_unknown += sum(
             1 if col.pipe_bounds == PipeBounds.UNKNOWN else 0 for col in row
         )
+    # extra: show unknowns:
+    for row in pipes:
+        for col in row:
+            if col.pipe_bounds == PipeBounds.UNKNOWN:
+                col.pipe_bounds = PipeBounds.INSIDE
+    print(small_map)
+
     return total_unknown
 
 
diff --git a/day10/lib/direction.py b/day10/lib/direction.py
index d8eb81a..eac6cd5 100644
--- a/day10/lib/direction.py
+++ b/day10/lib/direction.py
@@ -7,10 +7,6 @@ class Direction(Enum):
     SOUTH = 2
     EAST = 3
     WEST = 4
-    NORTH_EAST = 5
-    NORTH_WEST = 6
-    SOUTH_EAST = 7
-    SOUTH_WEST = 8
 
     def opposite(self) -> "Direction":
         if self == Direction.NORTH:
@@ -21,4 +17,4 @@ def opposite(self) -> "Direction":
             return Direction.WEST
         if self == Direction.WEST:
             return Direction.EAST
-        raise RuntimeError("invalid direction")
+        raise AssertionError("invalid direction")
diff --git a/day10/lib/pipes.py b/day10/lib/pipes.py
index 42d9f29..61fa42d 100644
--- a/day10/lib/pipes.py
+++ b/day10/lib/pipes.py
@@ -78,7 +78,7 @@ def next_position(
     def position(self) -> Position:
         return Position(self.row, self.col)
 
-    def __hash__(self) -> int:
+    def __hash__(self) -> int:  # pragma: no cover
         return hash(f"{self.row},{self.col}")
 
 
@@ -95,11 +95,16 @@ def __post_init__(self) -> None:
 
     def get_pipe(self, position: Position) -> Pipe:
         """returns a pipe given its position"""
+        if not self.is_in_map(position):
+            raise ValueError(f"Position outside map {position}")
         return self.pipes[position.row][position.col]
 
+    def is_in_map(self, position: Position) -> bool:
+        return 0 <= position.row < self.height and 0 <= position.col < self.width
+
     def get_pipe_safe(self, position: Position) -> Pipe | None:
-        if 0 <= position.row < self.height and 0 <= position.col < self.width:
-            return self.get_pipe(position)
+        if self.is_in_map(position):
+            return self.pipes[position.row][position.col]
         return None
 
     def __str__(self) -> str:
diff --git a/day10/lib/position.py b/day10/lib/position.py
index cbaed32..1ae7a19 100644
--- a/day10/lib/position.py
+++ b/day10/lib/position.py
@@ -18,15 +18,8 @@ def next_position(self, direction: Direction) -> "Position":
             return Position(self.row, self.col - 1)
         elif direction == Direction.SOUTH:
             return Position(self.row + 1, self.col)
-        elif direction == Direction.NORTH_EAST:
-            return Position(self.row - 1, self.col + 1)
-        elif direction == Direction.NORTH_WEST:
-            return Position(self.row - 1, self.col - 1)
-        elif direction == Direction.SOUTH_WEST:
-            return Position(self.row + 1, self.col - 1)
-        elif direction == Direction.SOUTH_EAST:
-            return Position(self.row + 1, self.col + 1)
-        raise ValueError(f"invalid direction {direction}")
+
+        raise AssertionError(f"invalid direction {direction}")
 
     def __hash__(self) -> int:
         return hash(f"{self.row}:{self.col}")
diff --git a/day10/tests/input-e.txt b/day10/tests/input-e.txt
new file mode 100644
index 0000000..81c221b
--- /dev/null
+++ b/day10/tests/input-e.txt
@@ -0,0 +1,5 @@
+..F7.
+.FJ|.
+FJ.L7
+|F--J
+LJ...
diff --git a/day10/tests/input-f.txt b/day10/tests/input-f.txt
new file mode 100644
index 0000000..7a4ef17
--- /dev/null
+++ b/day10/tests/input-f.txt
@@ -0,0 +1,5 @@
+S.F7.
+.FJ|.
+FJ.L7
+|F--J
+LJ...
diff --git a/day10/tests/test_day10.py b/day10/tests/test_day10.py
index cfa567b..c755d9e 100644
--- a/day10/tests/test_day10.py
+++ b/day10/tests/test_day10.py
@@ -1,16 +1,60 @@
-from day10.day10 import INPUT_A, INPUT_B, INPUT_C, INPUT_D, part1, part2, read_input
+from typing import TYPE_CHECKING
+
+import pytest
+
+from day10.day10 import (
+    INPUT_A,
+    INPUT_B,
+    INPUT_C,
+    INPUT_D,
+    calculate_s,
+    expand_pipe,
+    find_s,
+    part1,
+    part2,
+    read_input,
+)
+from day10.lib.position import Position
+
+INPUT_E = "day10/tests/input-e.txt"
+INPUT_F = "day10/tests/input-f.txt"
+
+
+if TYPE_CHECKING:
+    from day10.lib.pipes import PipeMap
 
 
 def test_day10() -> None:
-    pipe_map_a = read_input(INPUT_A)
-    pipe_map_b = read_input(INPUT_B)
+    pipe_map_a: PipeMap = read_input(INPUT_A)
+    pipe_map_b: PipeMap = read_input(INPUT_B)
     # q1
     assert part1(pipe_map_a) == 4
     assert part1(pipe_map_b) == 8
 
+    s_pos: Position = find_s(pipe_map_b)
+    assert s_pos == Position(2, 0)
+    assert calculate_s(s_pos, pipe_map_b) == "F"
+
     # q2
-    pipe_map_c = read_input(INPUT_C)
-    print(pipe_map_c)
+    pipe_map_c: PipeMap = read_input(INPUT_C)
     assert part2(pipe_map_c) == 4
-    pipe_map_d = read_input(INPUT_D)
+    pipe_map_d: PipeMap = read_input(INPUT_D)
     assert part2(pipe_map_d) == 8
+
+    # pipe_map no s
+    pipe_map_no_s: PipeMap = read_input(INPUT_E)
+    with pytest.raises(AssertionError):
+        s_pos = find_s(pipe_map_no_s)
+
+    # pipe map, s is incalculable
+    pipe_map_bad_s: PipeMap = read_input(INPUT_F)
+    s_pos = find_s(pipe_map_bad_s)
+
+    with pytest.raises(ValueError):
+        calculate_s(s_pos, pipe_map_no_s)
+
+    with pytest.raises(ValueError):
+        expand_pipe("^", True)
+
+    with pytest.raises(ValueError):
+        pipe_map_bad_s.get_pipe(Position(-1, -1))
diff --git a/pyproject.toml b/pyproject.toml
index dc1a74a..67fd26c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -38,6 +38,7 @@ exclude_lines = [
     "def main",
     "if TYPE_CHECKING:",
     "raise AssertionError",
+    "# pragma: no cover",
 ]
 omit = ["download_inputs.py", "maker.py"]
 precision = 2