t4001: add a test comparing basename similarity and content similarity

Add a simple test where a removed file is similar to two different added
files; one of them has the same basename, and the other has a slightly
higher content similarity.  In the current test, content similarity is
weighted higher than filename similarity.

Subsequent commits will add a new rule that weighs a mixture of filename
similarity and content similarity in a manner that will change the
outcome of this testcase.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4001-diff-rename.sh

@@ -262,4 +262,27 @@ test_expect_success 'diff-tree -l0 defaults to a big rename limit, not zero' '
 	grep "myotherfile.*myfile" actual
 '
 
+test_expect_success 'basename similarity vs best similarity' '
+	mkdir subdir &&
+	test_write_lines line1 line2 line3 line4 line5 \
+			 line6 line7 line8 line9 line10 >subdir/file.txt &&
+	git add subdir/file.txt &&
+	git commit -m "base txt" &&
+
+	git rm subdir/file.txt &&
+	test_write_lines line1 line2 line3 line4 line5 \
+			  line6 line7 line8 >file.txt &&
+	test_write_lines line1 line2 line3 line4 line5 \
+			  line6 line7 line8 line9 >file.md &&
+	git add file.txt file.md &&
+	git commit -a -m "rename" &&
+	git diff-tree -r -M --name-status HEAD^ HEAD >actual &&
+	# subdir/file.txt is 88% similar to file.md and 78% similar to file.txt
+	cat >expected <<-\EOF &&
+	R088	subdir/file.txt	file.md
+	A	file.txt
+	EOF
+	test_cmp expected actual
+'
+
 test_done