test: Add test that demands 3-way apply

This test case has a specially crafted patch that will only apply correctly
when a 3-way merge is performed.

Author: jpgrayson

t/t3402-pick-3way.sh

@@ -0,0 +1,144 @@
+#!/bin/sh
+test_description='Test pick that requires 3-way application'
+
+. ./test-lib.sh
+
+# The base version of the file has two identical sections.
+cat > file <<EOF
+1
+2
+3
+4
+5
+6
+7
+8
+
+1
+2
+3
+4
+5
+6
+7
+8
+
+EOF
+test_expect_success \
+    'Setup master branch' '
+    git add file &&
+    git commit -m "Add file" &&
+    stg init
+'
+
+test_expect_success \
+    'Make another branch' '
+    stg branch --create pickle
+'
+
+# The pickle branch adds prefix lines file has two identical sections.
+# These prefix lines will confuse a non-3-way merge by making the hunk
+# context look like it should go with the first "1-8" section.
+cat > file <<EOF
+101
+102
+103
+104
+105
+106
+107
+108
+
+1
+2
+3
+4
+5
+6
+7
+8
+
+1
+2
+3
+4
+5
+6
+7
+8
+
+EOF
+test_expect_success \
+    'Add prefix lines in pickle branch' '
+    stg new -rm muddy &&
+    stg branch master
+'
+
+# The master branch gets a tricky patch that inserts into the second
+# of the identical "1-8" sections.
+cat > file <<EOF
+1
+2
+3
+4
+5
+6
+7
+8
+
+1
+2
+3
+4
+tricky change
+5
+6
+7
+8
+
+EOF
+test_expect_success \
+    'Make patch with tricky diff' '
+    stg new -rm tricky
+'
+
+# A 3-way merge will reach this correct merge result. Without a 3-way merge,
+# the "tricky change" will be inserted in the first 1-8 section.
+cat > expected <<EOF
+101
+102
+103
+104
+105
+106
+107
+108
+
+1
+2
+3
+4
+5
+6
+7
+8
+
+1
+2
+3
+4
+tricky change
+5
+6
+7
+8
+
+EOF
+test_expect_success \
+    'Pick and apply tricky patch' '
+    stg branch pickle &&
+    stg pick -B master tricky &&
+    test_cmp expected file
+'
+
+test_done