Add further test of PMFG

Author: josephcbradley

test/spanningtrees/planar_maximally_filtered_graph.jl

@@ -31,4 +31,18 @@
     C = X' * X
     p = planar_maximally_filtered_graph(g, C)
     @test typeof(p) == SimpleGraph{eltype(g)}
-end
+
+    #Test that MST is a subset of the PMFG 
+    N = 50
+    X = rand(N, N); D = X'*X
+    c = complete_graph(N)
+    p = planar_maximally_filtered_graph(c, D)
+    mst_edges = kruskal_mst(c, D)
+    is_subgraph = true 
+    for mst_edge in mst_edges
+        if mst_edge ∉ edges(p)
+            is_subgraph = false
+        end
+    end
+    @test is_subgraph
+end