tests/int/env.bats: add test for runc exec -p

All existing tests check runc run, and there is no single runc exec
environment test except for one in exec.bats.

Add it (no new issues found).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

tests/integration/env.bats

@@ -95,3 +95,34 @@ function teardown() {
 	#
 	[ "$(wc -l <<<"$output")" -eq 4 ]
 }
+
+# Check that runc exec -p process.json takes env from
+# process.json only, not from config.json, and that HOME
+# is always set.
+@test "env [runc exec -p]" {
+	runc run -d --console-socket "$CONSOLE_SOCKET" test_busybox
+	[ "$status" -eq 0 ]
+
+	cat <<_EOF_ >process.json
+{
+    "terminal": false,
+    "args": [
+        "/bin/env"
+    ],
+    "cwd": "/",
+    "env": [
+        "FOO=bar"
+    ]
+}
+_EOF_
+
+	runc exec -p process.json test_busybox
+	[ "$status" -eq 0 ]
+	# Env should have entries from process.json.
+	[[ "$output" == *'FOO=bar'* ]]
+	# ...and HOME set from container's /etc/passwd.
+	[[ "$output" == *'HOME=/root'* ]]
+	# Env should NOT contain entries from config.json.
+	[[ "$output" != *'TERM='* ]]
+	[[ "$output" != *'PATH='* ]]
+}