Add lsdiff tests for missing features

Add five new test cases for lsdiff features that were previously
untested:

- lsdiff-number-files: Test -N/--number-files option
- lsdiff-files-range: Test -F/--files=RANGE option
- lsdiff-empty-files-removed: Test -E/--empty-files-as-removed option
- lsdiff-addprefix: Test --addprefix option
- lsdiff-strip-match: Test -p/--strip-match option

All tests pass with the traditional filterdiff.c implementation.

With scanner-based patchfilter (--enable-scanner-patchfilter), three
tests pass (number-files, files-range, addprefix) and two are marked
as XFAIL since those features are not yet implemented in scanner-based
lsdiff (empty-files-removed, strip-match).

Assisted-by: Claude Code

Author: twaugh

Makefile.am

@@ -290,6 +290,11 @@ TESTS = tests/newline1/run-test \
 	tests/lsdiff13/run-test \
 	tests/lsdiff14/run-test \
 	tests/lsdiff15/run-test \
+	tests/lsdiff-number-files/run-test \
+	tests/lsdiff-files-range/run-test \
+	tests/lsdiff-empty-files-removed/run-test \
+	tests/lsdiff-addprefix/run-test \
+	tests/lsdiff-strip-match/run-test \
 	tests/lsdiff-hunks-option/run-test \
 	tests/lsdiff-lines-option/run-test \
 	tests/lsdiff-exclusion-combined/run-test \
@@ -459,6 +464,14 @@ XFAIL_TESTS += \
   tests/grepdiff-annotate/run-test
 endif
 
+# lsdiff tests: expected to fail when scanner-patchfilter is enabled
+# (features not yet implemented in scanner-based lsdiff)
+if USE_SCANNER_PATCHFILTER
+XFAIL_TESTS += \
+  tests/lsdiff-empty-files-removed/run-test \
+  tests/lsdiff-strip-match/run-test
+endif
+
 test-perms: src/combinediff$(EXEEXT) src/flipdiff$(EXEEXT) \
 		src/lsdiff$(EXEEXT) src/grepdiff$(EXEEXT) src/patchview$(EXEEXT) \
 		scripts/splitdiff

tests/lsdiff-addprefix/run-test

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+# Test lsdiff --addprefix option
+
+. ${top_srcdir-.}/tests/common.sh
+
+cat << EOF > diff
+--- file1
++++ file1
+@@ -1 +1 @@
+-old
++new
+--- file2
++++ file2
+@@ -1 +1 @@
+-foo
++bar
+EOF
+
+${LSDIFF} --addprefix=prefix/ diff 2>errors >output || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output || exit 1
+prefix/file1
+prefix/file2
+EOF

tests/lsdiff-empty-files-removed/run-test

@@ -0,0 +1,44 @@
+#!/bin/sh
+
+# Test lsdiff -E/--empty-files-as-removed option
+
+. ${top_srcdir-.}/tests/common.sh
+
+# Create diffs where files become empty or start empty
+mkdir dir dir.orig
+
+# File that becomes empty (modified -> empty)
+echo content > dir.orig/becomes-empty
+touch dir/becomes-empty
+
+# File that starts empty (empty -> modified)
+touch dir.orig/was-empty
+echo content > dir/was-empty
+
+# Normal modification
+echo old > dir.orig/modified
+echo new > dir/modified
+
+${DIFF} -uN dir.orig dir > diff
+
+# Without -E, files that are/become empty show as modifications
+${LSDIFF} -s --strip=1 diff 2>errors >output1 || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output1 || exit 1
+! becomes-empty
+! modified
+! was-empty
+EOF
+
+# With -E, treat empty files as absent
+# becomes-empty: content->empty = treated as removal
+# was-empty: empty->content = treated as addition
+${LSDIFF} -sE --strip=1 diff 2>errors >output2 || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output2 || exit 1
+- becomes-empty
+! modified
++ was-empty
+EOF

tests/lsdiff-files-range/run-test

@@ -0,0 +1,63 @@
+#!/bin/sh
+
+# Test lsdiff -F/--files=RANGE option
+
+. ${top_srcdir-.}/tests/common.sh
+
+cat << EOF > diff
+--- file1
++++ file1
+@@ -1 +1 @@
+-old
++new
+--- file2
++++ file2
+@@ -1 +1 @@
+-foo
++bar
+--- file3
++++ file3
+@@ -1 +1 @@
+-test
++result
+--- file4
++++ file4
+@@ -1 +1 @@
+-data
++value
+EOF
+
+# Test single file
+${LSDIFF} -F2 diff 2>errors >output1 || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output1 || exit 1
+file2
+EOF
+
+# Test range
+${LSDIFF} -F2-3 diff 2>errors >output2 || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output2 || exit 1
+file2
+file3
+EOF
+
+# Test open-ended range
+${LSDIFF} -F3- diff 2>errors >output3 || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output3 || exit 1
+file3
+file4
+EOF
+
+# Test exclusion range
+${LSDIFF} -Fx2-3 diff 2>errors >output4 || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output4 || exit 1
+file1
+file4
+EOF

tests/lsdiff-number-files/run-test

@@ -0,0 +1,32 @@
+#!/bin/sh
+
+# Test lsdiff -N/--number-files option
+
+. ${top_srcdir-.}/tests/common.sh
+
+cat << EOF > diff
+--- file1
++++ file1
+@@ -1 +1 @@
+-old
++new
+--- file2
++++ file2
+@@ -1 +1 @@
+-foo
++bar
+--- file3
++++ file3
+@@ -1 +1 @@
+-test
++result
+EOF
+
+${LSDIFF} -N diff 2>errors >output || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output || exit 1
+File #1  	file1
+File #2  	file2
+File #3  	file3
+EOF

tests/lsdiff-strip-match/run-test

@@ -0,0 +1,43 @@
+#!/bin/sh
+
+# Test lsdiff -p/--strip-match option
+
+. ${top_srcdir-.}/tests/common.sh
+
+cat << EOF > diff
+--- a/src/file1.c
++++ b/src/file1.c
+@@ -1 +1 @@
+-old
++new
+--- a/docs/readme.txt
++++ b/docs/readme.txt
+@@ -1 +1 @@
+-old
++new
+--- a/src/file2.c
++++ b/src/file2.c
+@@ -1 +1 @@
+-old
++new
+EOF
+
+# Use -p to strip 'a/' and 'b/' prefixes when matching
+# Include only files in src/ directory
+# Note: -p affects matching, output still shows original paths from diff
+${LSDIFF} -p1 -i 'src/*' diff 2>errors >output || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output || exit 1
+a/src/file1.c
+a/src/file2.c
+EOF
+
+# Test that we can use --strip to also strip output
+${LSDIFF} -p1 -i 'src/*' --strip=1 diff 2>errors >output2 || exit 1
+[ -s errors ] && exit 1
+
+cat << EOF | cmp - output2 || exit 1
+src/file1.c
+src/file2.c
+EOF