Bisect: implement "git bisect run <cmd>..." to automatically bisect.

This idea was suggested by Bill Lear
(Message-ID: <17920.38942.364466.642979@lisa.zopyra.com>)
and I think it is a very good one.

This patch adds a new test file for "git bisect run", but there
is currently only one basic test.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t6030-bisect-run.sh

@@ -0,0 +1,57 @@
+#!/bin/sh
+#
+# Copyright (c) 2007 Christian Couder
+#
+test_description='Tests git-bisect run functionality'
+
+. ./test-lib.sh
+
+add_line_into_file()
+{
+    _line=$1
+    _file=$2
+
+    if [ -f "$_file" ]; then
+        echo "$_line" >> $_file || return $?
+        MSG="Add <$_line> into <$_file>."
+    else
+        echo "$_line" > $_file || return $?
+        git add $_file || return $?
+        MSG="Create file <$_file> with <$_line> inside."
+    fi
+
+    git-commit -m "$MSG" $_file
+}
+
+HASH1=
+HASH3=
+HASH4=
+
+test_expect_success \
+    'set up basic repo with 1 file (hello) and 4 commits' \
+    'add_line_into_file "1: Hello World" hello &&
+     add_line_into_file "2: A new day for git" hello &&
+     add_line_into_file "3: Another new day for git" hello &&
+     add_line_into_file "4: Ciao for now" hello &&
+     HASH1=$(git rev-list HEAD | tail -1) &&
+     HASH3=$(git rev-list HEAD | head -2 | tail -1) &&
+     HASH4=$(git rev-list HEAD | head -1)'
+
+# We want to automatically find the commit that
+# introduced "Another" into hello.
+test_expect_success \
+    'git bisect run simple case' \
+    'echo "#!/bin/sh" > test_script.sh &&
+     echo "grep Another hello > /dev/null" >> test_script.sh &&
+     echo "test \$? -ne 0" >> test_script.sh &&
+     chmod +x test_script.sh &&
+     git bisect start &&
+     git bisect good $HASH1 &&
+     git bisect bad $HASH4 &&
+     git bisect run ./test_script.sh > my_bisect_log.txt &&
+     grep "$HASH3 is first bad commit" my_bisect_log.txt'
+
+#
+#
+test_done
+