testsuite: add coverage for instance size override

Problem: there is no test coverage for broker bootstrap
with a PMI size less than the actual size.

Add some tests.

t/Makefile.am

@@ -95,6 +95,7 @@ TESTSCRIPTS = \
 	t0022-jj-reader.t \
 	t0023-jobspec1-validate.t \
 	t0026-flux-R.t \
+	t0033-size-override.t \
 	t1000-kvs.t \
 	t1001-kvs-internals.t \
 	t1003-kvs-stress.t \

t/t0033-size-override.t

@@ -0,0 +1,52 @@
+#!/bin/sh
+#
+
+test_description='Test instance size override'
+
+. `dirname $0`/sharness.sh
+
+test_expect_success 'size override fails if too small' '
+	test_must_fail flux broker \
+	    -Sbroker.rc1_path= -Sbroker.rc3_path= \
+	    -Ssize=1,-Sbroker.quorum=1 /bin/true 2>toosmall.err &&
+	grep "may only be increased" toosmall.err
+'
+test_expect_success 'an instance can be started with an extra rank' '
+	flux broker \
+	    -Sbroker.rc1_path= -Sbroker.rc3_path= \
+	    -Ssize=2 -Sbroker.quorum=1 \
+	    flux overlay status --no-pretty >overlay.out
+'
+test_expect_success 'flux overlay status shows the extra rank offline' '
+	grep "1 extra0: offline" overlay.out
+'
+test_expect_success 'an instance can be started with PMI plus extra' '
+	flux start -s2 -o,-Stbon.topo=kary:0 \
+	    -o,-Sbroker.rc1_path=,-Sbroker.rc3_path= \
+	    -o,-Ssize=3,-Sbroker.quorum=2 \
+	    flux overlay status --no-pretty >overlay2.out
+'
+test_expect_success 'flux overlay status shows the extra rank offline' '
+	grep "2 extra0: offline" overlay2.out
+'
+test_expect_success 'create config with fake resources' '
+	cat >fake.toml <<-EOT
+	[resource]
+	noverify = true
+	[[resource.config]]
+	hosts = "a,b,c"
+	cores = "0"
+	EOT
+'
+test_expect_success 'start full 2-broker instance with one extra rank' '
+	flux start -s2 -o,-Ssize=3,-Sbroker.quorum=2,-cfake.toml \
+	    flux resource status -s offline -no {nnodes} >offline.out
+'
+test_expect_success 'flux resource status reports one node offline' '
+	cat >offline.exp <<-EOT &&
+	1
+	EOT
+	test_cmp offline.exp offline.out
+'
+
+test_done