t5318: extract helpers to lib-commit-graph.sh

The graph_git_behavior helper is useful for testing that certain Git
commands behave the same when using the commit-graph and when not using
the commit-graph. Extract it to a new lib-commit-graph.sh file for use
in new test scripts that will split out from t5318.

While doing this extraction, also extract graph_read_expect and the
logic for priming the test_oid_cache.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/lib-commit-graph.sh

@@ -0,0 +1,48 @@
+#!/bin/sh
+
+# Helper functions for testing commit-graphs.
+
+# Initialize OID cache with oid_version
+test_oid_cache <<-EOF
+oid_version sha1:1
+oid_version sha256:2
+EOF
+
+graph_git_two_modes() {
+	git -c core.commitGraph=true $1 >output &&
+	git -c core.commitGraph=false $1 >expect &&
+	test_cmp expect output
+}
+
+graph_git_behavior() {
+	MSG=$1
+	DIR=$2
+	BRANCH=$3
+	COMPARE=$4
+	test_expect_success "check normal git operations: $MSG" '
+		cd "$TRASH_DIRECTORY/$DIR" &&
+		graph_git_two_modes "log --oneline $BRANCH" &&
+		graph_git_two_modes "log --topo-order $BRANCH" &&
+		graph_git_two_modes "log --graph $COMPARE..$BRANCH" &&
+		graph_git_two_modes "branch -vv" &&
+		graph_git_two_modes "merge-base -a $BRANCH $COMPARE"
+	'
+}
+
+graph_read_expect() {
+	OPTIONAL=""
+	NUM_CHUNKS=3
+	if test -n "$2"
+	then
+		OPTIONAL=" $2"
+		NUM_CHUNKS=$((3 + $(echo "$2" | wc -w)))
+	fi
+	cat >expect <<- EOF
+	header: 43475048 1 $(test_oid oid_version) $NUM_CHUNKS 0
+	num_commits: $1
+	chunks: oid_fanout oid_lookup commit_metadata$OPTIONAL
+	options:
+	EOF
+	test-tool read-graph >output &&
+	test_cmp expect output
+}