Add constructvariable! test

test/variable.jl

@@ -14,6 +14,21 @@ using JuMP
 import JuMP.repl
 using Base.Test
 
+mutable struct MyVariable
+    haslb::Bool
+    lowerbound::Number
+    hasub::Bool
+    upperbound::Number
+    hasfix::Bool
+    fixedvalue::Number
+    binary::Bool
+    integer::Bool
+    name::String
+    hasstart::Bool
+    start::Number
+    test_kw::Int
+end
+
 @testset "Variables" begin
     @testset "constructors" begin
         # Constructors
@@ -311,6 +326,44 @@ end
         @test JuMP.numvar(m) == 4
     end
 
+    @testset "Extension of @variable with constructvariable! #1029" begin
+        JuMP.variabletype(m::Model, ::Type{MyVariable}) = MyVariable
+        function JuMP.constructvariable!(m::Model, ::Type{MyVariable}, _error::Function, args...; test_kw::Int = 0)
+            MyVariable(args..., test_kw)
+        end
+        m = Model()
+        @variable(m, 1 <= x <= 2, MyVariable, binary = true, test_kw = 1, start = 3)
+        @test isa(x, MyVariable)
+        @test x.haslb
+        @test x.lowerbound == 1
+        @test x.hasub
+        @test x.upperbound == 2
+        @test !x.hasfix
+        @test isnan(x.fixedvalue)
+        @test x.binary
+        @test !x.integer
+        @test x.name == "x"
+        @test x.hasstart
+        @test x.start == 3
+        @test x.test_kw == 1
+        @variable(m, y[1:3] >= 0, MyVariable, test_kw = 2)
+        @test isa(y, Vector{MyVariable})
+        for i in 1:3
+            @test y[i].haslb
+            @test y[i].lowerbound == 0
+            @test !y[i].hasub
+            @test y[i].upperbound == Inf
+            @test !y[i].hasfix
+            @test isnan(y[i].fixedvalue)
+            @test !y[i].binary
+            @test !y[i].integer
+            @test y[i].name == "y[$i]"
+            @test !y[i].hasstart
+            @test isnan(y[i].start)
+            @test y[i].test_kw == 2
+        end
+    end
+
     # TODO decide what to do here
     # @testset "getstart on sparse array (#889)" begin
     #     m = Model()