Added tests for time solver interface

test/core/test_time_solvers.jl

@@ -0,0 +1,33 @@
+@testitem "time solver interface" begin
+    struct MyCustomDataHandler <: Peridynamics.AbstractDataHandler end
+    struct MyCustomTimeSolver <: Peridynamics.AbstractTimeSolver end
+    struct MyCustomSystem <: Peridynamics.AbstractSystem end
+    dh = MyCustomDataHandler()
+    solver = MyCustomTimeSolver()
+    system = MyCustomSystem()
+
+    @test_throws MethodError Peridynamics.init_time_solver!(solver, dh)
+
+    @test_throws ErrorException Peridynamics.solve!(dh, solver, Dict())
+
+    @test_throws Peridynamics.InterfaceError begin
+        Peridynamics.req_point_data_fields_timesolver(Peridynamics.AbstractTimeSolver)
+    end
+
+    @test_throws Peridynamics.InterfaceError begin
+        Peridynamics.req_bond_data_fields_timesolver(Peridynamics.AbstractTimeSolver)
+    end
+
+    @test_throws Peridynamics.InterfaceError begin
+        Peridynamics.req_data_fields_timesolver(Peridynamics.AbstractTimeSolver)
+    end
+
+    @test isnothing(Peridynamics.init_field_solver(solver, system, Val(:myrandomfield)))
+end
+
+@testitem "required fields all timesolvers" begin
+    req_fields_solvers = (:position, :displacement, :velocity, :velocity_half,
+                          :acceleration, :b_int, :b_ext, :velocity_half_old, :b_int_old,
+                          :density_matrix)
+    @test Peridynamics.required_fields_timesolvers() === req_fields_solvers
+end