solve! returns the problem (#658)

Author: ericphanson

src/solution.jl

@@ -65,7 +65,7 @@ end
 
 Solves the problem, populating `problem.optval` with the optimal value, as well
 as the values of the variables (accessed by [`evaluate`](@ref)) and constraint
-duals (accessed by `cons.dual`), where applicable.
+duals (accessed by `cons.dual`), where applicable. Returns the input `problem`.
 
 Optional keyword arguments:
 
@@ -134,7 +134,7 @@ function solve!(
             populate_dual!(context.model, c, indices)
         end
     end
-    return
+    return p
 end
 
 function populate_dual!(::MOI.ModelLike, c::Constraint, ::Nothing)

test/test_utilities.jl

@@ -42,7 +42,7 @@ function solve_and_return_output(problem, solver; kwargs...)
     return fetch(out_task)
 end
 
-function test_solve!_does_not_return_anything()
+function test_solve!_returns_the_problem()
     x = Variable()
     p = satisfy(x >= 0)
     output = solve!(
@@ -53,7 +53,7 @@ function test_solve!_does_not_return_anything()
             "eps_abs" => 1e-6,
         ),
     )
-    @test output === nothing
+    @test output === p
     return
 end
 
@@ -85,7 +85,7 @@ function test_solve!_can_take_an_optimizer_directly()
             "eps_abs" => 1e-6,
         ),
     )
-    @test output === nothing
+    @test output === p
     return
 end