Fixed test in acset2symbolics

Added a fix to the acset2symbolics code that helps fix the issue caused there by #77. A full fix to this issue can restore the code to just use infer_terminal_names

src/acset2symbolic.jl

@@ -43,11 +43,13 @@ end
 # e.g. ∂ₜ(G) == κ*u becomes ∂ₜ(G) == u*κ
 function merge_equations(d::SummationDecapode)
   eqn_lookup, terminal_eqns = Dict(), SymEqSym[]
+  deriv_op_tgts = d[incident(d, DerivOp, :op1), [:tgt, :name]] # Patches over issue #77
+  terminal_vars = Set{Symbol}(vcat(infer_terminal_names(d), deriv_op_tgts))
 
   foreach(to_symbolics(d)) do x
     sub = SymbolicUtils.substitute(x.rhs, eqn_lookup)
     push!(eqn_lookup, (x.lhs => sub))
-    if x.lhs.name in infer_terminal_names(d)
+    if x.lhs.name in terminal_vars
       push!(terminal_eqns, SymEqSym(x.lhs, sub))
     end
   end

test/acset2symbolic.jl

@@ -96,7 +96,7 @@ using Catlab
     c_exp == ∂ₜ(c_exp)
   end
 
-  @test_broken repeated_vars == symbolic_rewriting(self_changing)
+  @test self_changing == symbolic_rewriting(self_changing)
 
   literal = @decapode begin
     A::Form0