test: Add tests for CPU and memory graph pages

This makes sure that the page configures as expected and doesn't crash.

Don't test the innards of the graph again, as they are exactly the same
widgets as the ones already tested further above. But do ensure that
they have a reasonable size.

Reproduces https://bugzilla.redhat.com/show_bug.cgi?id=1792623

Closes cockpit-project#13439

test/verify/check-metrics

@@ -168,6 +168,41 @@ class TestMetrics(MachineCase):
 
         m.execute("kill %d" % net_pid)
 
+        if m.image in ["rhel-8-2-distropkg"]:
+            return  # HACK: individual graph pages broken, fixed in PR #13438
+
+        el_width = "(function (sel) { return ph_find(sel).offsetWidth; })"
+        el_height = "(function (sel) { return ph_find(sel).offsetHeight; })"
+
+        # CPU graph page
+        b.click("#link-cpu")
+        b.wait_not_visible(".ct-graph-memory")
+        b.wait_visible("#cpu_status_title")
+        b.wait_visible("#cpu_status_graph")
+        self.assertGreater(b.call_js_func(el_width, "#cpu_status_graph"), 500)
+        self.assertGreater(b.call_js_func(el_height, "#cpu_status_graph"), 300)
+        b.wait_visible(".server-graph-legend .cpu-kernel")
+
+        # go back to graphs overview
+        b.click("#graphs-link")
+        b.wait_visible(".ct-graph-memory")
+        b.wait_visible(".ct-graph-cpu")
+
+        # memory graph page
+        if m.image in ["fedora-coreos", "ubuntu-1804", "ubuntu-stable", "debian-stable", "debian-testing"]:
+            # no swap on these
+            b.wait_not_visible("#link-memory-and-swap")
+            b.click("#link-memory")
+        else:
+            b.wait_not_visible("#link-memory")
+            b.click("#link-memory-and-swap")
+        b.wait_not_visible(".ct-graph-cpu")
+        b.wait_visible("#memory_status_title")
+        b.wait_visible("#memory_status_graph")
+        self.assertGreater(b.call_js_func(el_width, "#memory_status_graph"), 500)
+        self.assertGreater(b.call_js_func(el_height, "#memory_status_graph"), 300)
+        b.wait_visible(".server-graph-legend .memory-used")
+
     @skipImage("No PCP available", "fedora-coreos")
     def testPcp(self):
         m = self.machine