tests: give vcs-svn/line_buffer its own test script

Split the line_buffer test into small pieces and move it to its
own file as preparation for adding more tests.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>

t/t0081-line-buffer.sh

@@ -0,0 +1,67 @@
+#!/bin/sh
+
+test_description="Test the svn importer's input handling routines.
+"
+. ./test-lib.sh
+
+test_expect_success 'read greeting' '
+	echo HELLO >expect &&
+	test-line-buffer <<-\EOF >actual &&
+	read 5
+	HELLO
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '0-length read, send along greeting' '
+	printf "%s\n" "" HELLO >expect &&
+	test-line-buffer <<-\EOF >actual &&
+	read 0
+
+	copy 5
+	HELLO
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'buffer_read_string copes with trailing null byte' '
+	echo >expect &&
+	q_to_nul <<-\EOF | test-line-buffer >actual &&
+	read 1
+	Q
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success '0-length read, copy null byte' '
+	printf "%s\n" "" Q | q_to_nul >expect &&
+	q_to_nul <<-\EOF | test-line-buffer >actual &&
+	read 0
+
+	copy 1
+	Q
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'long reads are truncated' '
+	printf "%s\n" foo "" >expect &&
+	test-line-buffer <<-\EOF >actual &&
+	read 5
+	foo
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'long copies are truncated' '
+	printf "%s\n" "" foo >expect &&
+	test-line-buffer <<-\EOF >actual &&
+	read 0
+
+	copy 5
+	foo
+	EOF
+	test_cmp expect actual
+'
+
+test_done