ref AAAAACCCCCGGGGGTTTTT
    12345678901234567890

Test files for read pairs.

Starting letter:
a = both start/end differ
b = only ends differ
c = only start differ
d = both start/end match

Each file has two versions (eg a7 and a7b) which are identical except
for read ordering with the entries swapping lines.  (This may make some
data unsorted.)

We also have neighbouring pairs (a7/a8, a9/a10) which are the same
coordinates, but flipping the orientation of READ1 and READ2.
Eg pointing inwards vs pointing outwards.



Starts and ends differ:

Combinations: (2) R1 before R2?
              (2) R1 starts before R2?
              (2) R1 ends before R2?
              (2) R1 top, R2 bottom (vs vice versa)?
              => 16

a7            a8
1--->         <---1
   <---2         2--->

2--->         <---2
   <---1         1--->

a7b           a8b
   <---2         2--->
1--->         <---1

   <---1         1--->
2--->         <---2

a9            a10
1------>      <------1
  <--2          2-->

2------>      <------2
  <--1          1-->

a9b           a10b
  <--2          2-->
1------>      <------1

  <--1          1-->
2------>      <------2



Starts match, ends differ:

b7            b8
1--->         <---1
<------2      2------>

2--->         <---2
<------1      1------>

b7b           b8b
<------2      2------>
1--->         <---1

<------1      1------>
2--->         <---2

Starts differ, ends match:

c7            c8
1------>      <------1
   <---2         2--->

2------>      <------2
   <---1         1--->

c7b           c8b
   <---2         2--->
1------>      <------1

   <---1         1--->
2------>      <------2

Starts and ends both match:

d7
1------>
<------2

2------>
<------1

d7b
<------2
1------>

<------1
2------>

-----------------------------------------------------------------------------
Test files for read triplets

d4           d5
1----->      <-----1
<-----m      <-----m
<-----2      2----->

d4b          d5b
1----->      <-----1
<-----2      2----->
<-----m      <-----m

d4c          d5c
<-----2      2----->
<-----m      <-----m
1----->      <-----1

d4d          d5d
<-----2      2----->
1----->      <-----1
<-----m      <-----m

d4e          d5e
<-----m      <-----m
1----->      <-----1
<-----2      2----->

d4f          d5f
<-----m      <-----m
<-----2      2----->
1----->      <-----1


a4           a5
1--->        m--->
  m--->        1--->
    <---2        <---2

