diff --git a/src/data_format_conversions.jl b/src/data_format_conversions.jl
index 9883de97b8..9770b53f4b 100644
--- a/src/data_format_conversions.jl
+++ b/src/data_format_conversions.jl
@@ -98,7 +98,7 @@ function _convert_data!(
     ::Val{Symbol("3.0.0")},
     ::Val{Symbol("4.0.0")},
 )
-    for component in raw["data"]["components"]
+    for component in vcat(raw["data"]["components"], raw["data"]["masked_components"])
         if haskey(component, "operation_cost")
             op_cost = component["operation_cost"]
             if op_cost["__metadata__"]["type"] in COST_CONTAINERS &&
diff --git a/src/descriptors/power_system_structs.json b/src/descriptors/power_system_structs.json
index 6e225b0f0f..d987a18136 100644
--- a/src/descriptors/power_system_structs.json
+++ b/src/descriptors/power_system_structs.json
@@ -2704,7 +2704,7 @@
                     "name": "operation_cost",
                     "null_value": "TwoPartCost(nothing)",
                     "data_type": "OperationalCost",
-                    "default": "TwoPartCost(0.0, 0.0)",
+                    "default": "TwoPartCost(LinearFunctionData(0.0), 0.0)",
                     "comment": "Operation Cost of Generation [`OperationalCost`](@ref)"
                 },
                 {
@@ -3052,7 +3052,7 @@
                     "name": "operation_cost",
                     "null_value": "TwoPartCost(nothing)",
                     "data_type": "OperationalCost",
-                    "default": "TwoPartCost(0.0, 0.0)",
+                    "default": "TwoPartCost(LinearFunctionData(0.0), 0.0)",
                     "comment": "Operation Cost of Generation [`OperationalCost`](@ref)"
                 },
                 {
@@ -3220,7 +3220,7 @@
                     "name": "operation_cost",
                     "null_value": "TwoPartCost(nothing)",
                     "data_type": "OperationalCost",
-                    "default": "TwoPartCost(0.0, 0.0)",
+                    "default": "TwoPartCost(LinearFunctionData(0.0), 0.0)",
                     "comment": "Operation Cost of Generation [`OperationalCost`](@ref)"
                 },
                 {
@@ -3468,7 +3468,7 @@
                     "name": "operation_cost",
                     "null_value": "TwoPartCost(nothing)",
                     "data_type": "OperationalCost",
-                    "default": "TwoPartCost(0.0, 0.0)",
+                    "default": "TwoPartCost(LinearFunctionData(0.0), 0.0)",
                     "comment": "Operation Cost of Generation [`OperationalCost`](@ref)"
                 },
                 {
diff --git a/src/models/function_data.jl b/src/models/function_data.jl
index ffb76d5734..fae33a380d 100644
--- a/src/models/function_data.jl
+++ b/src/models/function_data.jl
@@ -50,8 +50,11 @@ end
 get_coefficients(fd::PolynomialFunctionData) = fd.coefficients
 
 function _validate_piecewise_x(x_coords)
-    (length(x_coords) >= 2) ||
-        throw(ArgumentError("Must specify at least two x-coordinates"))
+    # TODO currently there exist cases where we are constructing a PiecewiseLinearPointData
+    # with only one point (e.g., `calculate_variable_cost` within
+    # `power_system_table_data.jl`) -- what does this represent?
+    # (length(x_coords) >= 2) ||
+    #     throw(ArgumentError("Must specify at least two x-coordinates"))
     issorted(x_coords) || throw(ArgumentError("Piecewise x-coordinates must be ascending"))
     # TODO are there legitimate cases where we'd want negative x-coordinates?
     # (x_coords[1] >= 0) || throw(ArgumentError("Piecewise x-coordinates cannot be negative"))
diff --git a/src/models/generated/HydroDispatch.jl b/src/models/generated/HydroDispatch.jl
index c4b891d4d3..8b0a9e8d7f 100644
--- a/src/models/generated/HydroDispatch.jl
+++ b/src/models/generated/HydroDispatch.jl
@@ -79,11 +79,11 @@ mutable struct HydroDispatch <: HydroGen
     internal::InfrastructureSystemsInternal
 end
 
-function HydroDispatch(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, operation_cost=TwoPartCost(0.0, 0.0), services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
+function HydroDispatch(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
     HydroDispatch(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, operation_cost, services, dynamic_injector, ext, time_series_container, InfrastructureSystemsInternal(), )
 end
 
-function HydroDispatch(; name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, operation_cost=TwoPartCost(0.0, 0.0), services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
+function HydroDispatch(; name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
     HydroDispatch(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, operation_cost, services, dynamic_injector, ext, time_series_container, internal, )
 end
 
diff --git a/src/models/generated/HydroEnergyReservoir.jl b/src/models/generated/HydroEnergyReservoir.jl
index 09f70f9f28..137e5842e8 100644
--- a/src/models/generated/HydroEnergyReservoir.jl
+++ b/src/models/generated/HydroEnergyReservoir.jl
@@ -102,11 +102,11 @@ mutable struct HydroEnergyReservoir <: HydroGen
     internal::InfrastructureSystemsInternal
 end
 
-function HydroEnergyReservoir(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, storage_capacity, inflow, initial_storage, operation_cost=TwoPartCost(0.0, 0.0), storage_target=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
+function HydroEnergyReservoir(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, storage_capacity, inflow, initial_storage, operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), storage_target=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
     HydroEnergyReservoir(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, storage_capacity, inflow, initial_storage, operation_cost, storage_target, conversion_factor, time_at_status, services, dynamic_injector, ext, time_series_container, InfrastructureSystemsInternal(), )
 end
 
-function HydroEnergyReservoir(; name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, storage_capacity, inflow, initial_storage, operation_cost=TwoPartCost(0.0, 0.0), storage_target=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
+function HydroEnergyReservoir(; name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, storage_capacity, inflow, initial_storage, operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), storage_target=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
     HydroEnergyReservoir(name, available, bus, active_power, reactive_power, rating, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, base_power, storage_capacity, inflow, initial_storage, operation_cost, storage_target, conversion_factor, time_at_status, services, dynamic_injector, ext, time_series_container, internal, )
 end
 
diff --git a/src/models/generated/HydroPumpedStorage.jl b/src/models/generated/HydroPumpedStorage.jl
index 71a8312f32..d8f64c2a24 100644
--- a/src/models/generated/HydroPumpedStorage.jl
+++ b/src/models/generated/HydroPumpedStorage.jl
@@ -128,11 +128,11 @@ mutable struct HydroPumpedStorage <: HydroGen
     internal::InfrastructureSystemsInternal
 end
 
-function HydroPumpedStorage(name, available, bus, active_power, reactive_power, rating, base_power, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, rating_pump, active_power_limits_pump, reactive_power_limits_pump, ramp_limits_pump, time_limits_pump, storage_capacity, inflow, outflow, initial_storage, storage_target=(up=1.0, down=1.0), operation_cost=TwoPartCost(0.0, 0.0), pump_efficiency=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
+function HydroPumpedStorage(name, available, bus, active_power, reactive_power, rating, base_power, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, rating_pump, active_power_limits_pump, reactive_power_limits_pump, ramp_limits_pump, time_limits_pump, storage_capacity, inflow, outflow, initial_storage, storage_target=(up=1.0, down=1.0), operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), pump_efficiency=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
     HydroPumpedStorage(name, available, bus, active_power, reactive_power, rating, base_power, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, rating_pump, active_power_limits_pump, reactive_power_limits_pump, ramp_limits_pump, time_limits_pump, storage_capacity, inflow, outflow, initial_storage, storage_target, operation_cost, pump_efficiency, conversion_factor, time_at_status, services, dynamic_injector, ext, time_series_container, InfrastructureSystemsInternal(), )
 end
 
-function HydroPumpedStorage(; name, available, bus, active_power, reactive_power, rating, base_power, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, rating_pump, active_power_limits_pump, reactive_power_limits_pump, ramp_limits_pump, time_limits_pump, storage_capacity, inflow, outflow, initial_storage, storage_target=(up=1.0, down=1.0), operation_cost=TwoPartCost(0.0, 0.0), pump_efficiency=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
+function HydroPumpedStorage(; name, available, bus, active_power, reactive_power, rating, base_power, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, rating_pump, active_power_limits_pump, reactive_power_limits_pump, ramp_limits_pump, time_limits_pump, storage_capacity, inflow, outflow, initial_storage, storage_target=(up=1.0, down=1.0), operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), pump_efficiency=1.0, conversion_factor=1.0, time_at_status=INFINITE_TIME, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
     HydroPumpedStorage(name, available, bus, active_power, reactive_power, rating, base_power, prime_mover_type, active_power_limits, reactive_power_limits, ramp_limits, time_limits, rating_pump, active_power_limits_pump, reactive_power_limits_pump, ramp_limits_pump, time_limits_pump, storage_capacity, inflow, outflow, initial_storage, storage_target, operation_cost, pump_efficiency, conversion_factor, time_at_status, services, dynamic_injector, ext, time_series_container, internal, )
 end
 
diff --git a/src/models/generated/InterconnectingConverter.jl b/src/models/generated/InterconnectingConverter.jl
index 1f82d693dd..8f54312309 100644
--- a/src/models/generated/InterconnectingConverter.jl
+++ b/src/models/generated/InterconnectingConverter.jl
@@ -69,11 +69,11 @@ mutable struct InterconnectingConverter <: StaticInjection
     internal::InfrastructureSystemsInternal
 end
 
-function InterconnectingConverter(name, available, bus, dc_bus, active_power, rating, active_power_limits, base_power, operation_cost=TwoPartCost(0.0, 0.0), efficiency=1.0, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
+function InterconnectingConverter(name, available, bus, dc_bus, active_power, rating, active_power_limits, base_power, operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), efficiency=1.0, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), )
     InterconnectingConverter(name, available, bus, dc_bus, active_power, rating, active_power_limits, base_power, operation_cost, efficiency, services, dynamic_injector, ext, time_series_container, InfrastructureSystemsInternal(), )
 end
 
-function InterconnectingConverter(; name, available, bus, dc_bus, active_power, rating, active_power_limits, base_power, operation_cost=TwoPartCost(0.0, 0.0), efficiency=1.0, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
+function InterconnectingConverter(; name, available, bus, dc_bus, active_power, rating, active_power_limits, base_power, operation_cost=TwoPartCost(LinearFunctionData(0.0), 0.0), efficiency=1.0, services=Device[], dynamic_injector=nothing, ext=Dict{String, Any}(), time_series_container=InfrastructureSystems.TimeSeriesContainer(), internal=InfrastructureSystemsInternal(), )
     InterconnectingConverter(name, available, bus, dc_bus, active_power, rating, active_power_limits, base_power, operation_cost, efficiency, services, dynamic_injector, ext, time_series_container, internal, )
 end
 
diff --git a/src/parsers/power_models_data.jl b/src/parsers/power_models_data.jl
index f610357f6f..c15ae54c4c 100644
--- a/src/parsers/power_models_data.jl
+++ b/src/parsers/power_models_data.jl
@@ -322,7 +322,7 @@ end
 
 function make_hydro_gen(gen_name, d, bus, sys_mbase)
     ramp_agc = get(d, "ramp_agc", get(d, "ramp_10", get(d, "ramp_30", abs(d["pmax"]))))
-    curtailcost = TwoPartCost(0.0, 0.0)
+    curtailcost = TwoPartCost(LinearFunctionData(0.0), 0.0)
 
     base_conversion = sys_mbase / d["mbase"]
     return HydroDispatch(; # No way to define storage parameters for gens in PM so can only make HydroDispatch
@@ -438,7 +438,7 @@ function make_thermal_gen(gen_name::AbstractString, d::Dict, bus::ACBus, sys_mba
             fixed = max(0.0,
                 first_y - first(get_slopes(PiecewiseLinearPointData(points))) * first_x,
             )
-            cost = PiecewiseLinearPointData((x, y - fixed) for (x, y) in points)
+            cost = PiecewiseLinearPointData([(x, y - fixed) for (x, y) in points])
         elseif model == GeneratorCostModels.POLYNOMIAL
             # For now, we make the variable cost a PolynomialFunctionData with all but the
             # constant term and make the fixed cost the constant term; in a future update,
@@ -447,7 +447,7 @@ function make_thermal_gen(gen_name::AbstractString, d::Dict, bus::ACBus, sys_mba
             # This transforms [3.0, 1.0, 4.0, 2.0] into [(1, 4.0), (2, 1.0), (3, 3.0)]
             coeffs = enumerate(reverse(d["cost"][1:(end - 1)]))
             cost = PolynomialFunctionData(Dict((i, c / sys_mbase^i) for (i, c) in coeffs))
-            fixed = d["cost"][end]
+            fixed = (d["ncost"] >= 1) ? last(d["cost"]) : 0.0
         end
         startup = d["startup"]
         shutdn = d["shutdown"]
diff --git a/src/parsers/power_system_table_data.jl b/src/parsers/power_system_table_data.jl
index e6c20b7c69..048fbe014e 100644
--- a/src/parsers/power_system_table_data.jl
+++ b/src/parsers/power_system_table_data.jl
@@ -855,10 +855,11 @@ function calculate_variable_cost(
         for i in 2:length(var_cost)
             var_cost[i] = (var_cost[i - 1][1] + var_cost[i][1], var_cost[i][2])
         end
+    var_cost = PiecewiseLinearPointData([(x, y) for (y, x) in var_cost])
 
     elseif length(var_cost) == 1
         # if there is only one point, use it to determine the constant $/MW cost
-        var_cost = var_cost[1][1] * fuel_cost + vom
+        var_cost = LinearFunctionData(var_cost[1][1] * fuel_cost + vom)
         fixed = 0.0
     end
     return var_cost, fixed, fuel_cost
@@ -892,8 +893,9 @@ function calculate_variable_cost(
             (var_cost[2][1] + vom / (var_cost[2][2] - var_cost[1][2]) * var_cost[1][2]),
         )
         var_cost = [(var_cost[i][1] - fixed, var_cost[i][2]) for i in 1:length(var_cost)]
+        var_cost = PiecewiseLinearPointData([(x, y) for (y, x) in var_cost])
     elseif length(var_cost) == 1
-        var_cost = var_cost[1][1]
+        var_cost = LinearFunctionData(var_cost[1][1])
         fixed = 0.0
     end
 
@@ -1041,14 +1043,13 @@ function make_thermal_generator_multistart(
     base_power = get_base_power(thermal_gen)
     var_cost, fixed, fuel_cost =
         calculate_variable_cost(data, gen, cost_colnames, base_power)
-    if var_cost isa Float64
+    if var_cost isa LinearFunctionData
         no_load_cost = 0.0
-        var_cost = LinearFunctionData(var_cost)
     else
-        no_load_cost = var_cost[1][1]
+        (no_load_x, no_load_cost) = first(var_cost)
         var_cost =
             PiecewiseLinearPointData([
-                (c - no_load_cost, pp - var_cost[1][2]) for (c, pp) in var_cost
+                (pp - no_load_x, c - no_load_cost) for (pp, c) in var_cost
             ])
     end
     lag_hot =
diff --git a/test/data_14bus_pu.jl b/test/data_14bus_pu.jl
index 0f77d99396..7e64d4b4c4 100644
--- a/test/data_14bus_pu.jl
+++ b/test/data_14bus_pu.jl
@@ -654,7 +654,7 @@ thermal_generators14(nodes14) = [
         reactive_power_limits = (min = 0.0, max = 0.1),
         time_limits = nothing,
         ramp_limits = nothing,
-        operation_cost = ThreePartCost((430.292599, 2000.0), 0.0, 0.0, 0.0),
+        operation_cost = ThreePartCost(QuadraticFunctionData(430.292599, 2000.0, 0.0), 0.0, 0.0, 0.0),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -671,7 +671,7 @@ thermal_generators14(nodes14) = [
         reactive_power_limits = (min = -0.4, max = 0.5),
         time_limits = nothing,
         ramp_limits = nothing,
-        operation_cost = ThreePartCost((2500.0, 2000.0), 0.0, 0.0, 0.0),
+        operation_cost = ThreePartCost(QuadraticFunctionData(2500.0, 2000.0, 0.0), 0.0, 0.0, 0.0),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -688,7 +688,7 @@ thermal_generators14(nodes14) = [
         reactive_power_limits = (min = 0.0, max = 0.4),
         time_limits = nothing,
         ramp_limits = nothing,
-        operation_cost = ThreePartCost((100.0, 4000.0), 0.0, 0.0, 0.0),
+        operation_cost = ThreePartCost(QuadraticFunctionData(100.0, 4000.0, 0.0), 0.0, 0.0, 0.0),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -705,7 +705,7 @@ thermal_generators14(nodes14) = [
         reactive_power_limits = (min = -0.06, max = 0.24),
         time_limits = nothing,
         ramp_limits = nothing,
-        operation_cost = ThreePartCost((100.0, 4000.0), 0.0, 0.0, 0.0),
+        operation_cost = ThreePartCost(QuadraticFunctionData(100.0, 4000.0, 0.0), 0.0, 0.0, 0.0),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -722,7 +722,7 @@ thermal_generators14(nodes14) = [
         reactive_power_limits = (min = -0.06, max = 0.24),
         time_limits = nothing,
         ramp_limits = nothing,
-        operation_cost = ThreePartCost((100.0, 4000.0), 0.0, 0.0, 0.0),
+        operation_cost = ThreePartCost(QuadraticFunctionData(100.0, 4000.0, 0.0), 0.0, 0.0, 0.0),
         base_power = 100.0,
     ),
 ]
diff --git a/test/data_5bus_pu.jl b/test/data_5bus_pu.jl
index b92c1f8489..46105dcc5b 100644
--- a/test/data_5bus_pu.jl
+++ b/test/data_5bus_pu.jl
@@ -313,7 +313,7 @@ thermal_generators5(nodes5) = [
         reactive_power_limits = (min = -0.30, max = 0.30),
         time_limits = nothing,
         ramp_limits = nothing,
-        operation_cost = ThreePartCost((0.0, 1400.0), 0.0, 4.0, 2.0),
+        operation_cost = ThreePartCost(LinearFunctionData(1400.0), 0.0, 4.0, 2.0),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -330,7 +330,7 @@ thermal_generators5(nodes5) = [
         reactive_power_limits = (min = -1.275, max = 1.275),
         time_limits = (up = 0.02, down = 0.02),
         ramp_limits = (up = 2.0, down = 1.0),
-        operation_cost = ThreePartCost((0.0, 1500.0), 0.0, 1.5, 0.75),
+        operation_cost = ThreePartCost(LinearFunctionData(1500.0), 0.0, 1.5, 0.75),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -347,7 +347,7 @@ thermal_generators5(nodes5) = [
         reactive_power_limits = (min = -3.90, max = 3.90),
         time_limits = (up = 0.012, down = 0.012),
         ramp_limits = (up = 3.0, down = 2.0),
-        operation_cost = ThreePartCost((0.0, 3000.0), 0.0, 3.0, 1.5),
+        operation_cost = ThreePartCost(LinearFunctionData(3000.0), 0.0, 3.0, 1.5),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -364,7 +364,7 @@ thermal_generators5(nodes5) = [
         reactive_power_limits = (min = -1.5, max = 1.5),
         time_limits = (up = 0.015, down = 0.015),
         ramp_limits = (up = 2.0, down = 1.0),
-        operation_cost = ThreePartCost((0.0, 4000.0), 0.0, 4.0, 2.0),
+        operation_cost = ThreePartCost(LinearFunctionData(4000.0), 0.0, 4.0, 2.0),
         base_power = 100.0,
     ),
     ThermalStandard(;
@@ -381,7 +381,7 @@ thermal_generators5(nodes5) = [
         reactive_power_limits = (min = -4.50, max = 4.50),
         time_limits = (up = 0.015, down = 0.015),
         ramp_limits = (up = 5.0, down = 3.0),
-        operation_cost = ThreePartCost((0.0, 1000.0), 0.0, 1.5, 0.75),
+        operation_cost = ThreePartCost(LinearFunctionData(1000.0), 0.0, 1.5, 0.75),
         base_power = 100.0,
     ),
 ];
@@ -397,7 +397,7 @@ renewable_generators5(nodes5) = [
         PrimeMovers.WT,
         (min = 0.0, max = 0.0),
         1.0,
-        TwoPartCost(22.0, 0.0),
+        TwoPartCost(LinearFunctionData(22.0), 0.0),
         100.0,
     ),
     RenewableDispatch(
@@ -410,7 +410,7 @@ renewable_generators5(nodes5) = [
         PrimeMovers.WT,
         (min = 0.0, max = 0.0),
         1.0,
-        TwoPartCost(22.0, 0.0),
+        TwoPartCost(LinearFunctionData(22.0), 0.0),
         100.0,
     ),
     RenewableDispatch(
@@ -423,7 +423,7 @@ renewable_generators5(nodes5) = [
         PrimeMovers.WT,
         (min = -0.800, max = 0.800),
         1.0,
-        TwoPartCost(22.0, 0.0),
+        TwoPartCost(LinearFunctionData(22.0), 0.0),
         100.0,
     ),
 ];
@@ -459,7 +459,7 @@ hydro_generators5(nodes5) = [
         storage_capacity = 1.0,
         inflow = 0.2,
         initial_storage = 0.5,
-        operation_cost = TwoPartCost(15.0, 0.0),
+        operation_cost = TwoPartCost(LinearFunctionData(15.0), 0.0),
     ),
 ];
 
@@ -579,7 +579,7 @@ interruptible(nodes5) = [
         0.10,
         0.0,
         100.0,
-        TwoPartCost(150.0, 2400.0),
+        TwoPartCost(LinearFunctionData(150.0), 2400.0),
     ),
 ]
 
@@ -598,7 +598,7 @@ ordc5() = [
         true,
         0.6,
         TwoPartCost(
-            [(0.0, 9000.0), (0.2, 6000.0), (0.4, 500.0), (0.6, 10.0), (0.8, 0.0)],
+            [(0.0, 9000.0), (0.2, 6000.0), (0.4, 500.0), (0.6, 10.0), (0.8, 0.0)],  # TODO
             0.0,
         ),
     ),
diff --git a/test/runtests.jl b/test/runtests.jl
index 02ac00a124..48f38934d4 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -9,6 +9,7 @@ import InteractiveUtils
 import JSON3
 import PowerSystemCaseBuilder: PSYTestSystems
 import InfrastructureSystems
+import Random
 const IS = InfrastructureSystems
 using PowerSystems
 import PowerSystems: PowerSystemTableData
diff --git a/test/test_dynamic_generator.jl b/test/test_dynamic_generator.jl
index a65405828f..54748f0d6d 100644
--- a/test/test_dynamic_generator.jl
+++ b/test/test_dynamic_generator.jl
@@ -27,7 +27,7 @@ static_gen = ThermalStandard(;
     reactive_power_limits = (min = -0.30, max = 0.30),
     time_limits = nothing,
     ramp_limits = nothing,
-    operation_cost = ThreePartCost((0.0, 1400.0), 0.0, 4.0, 2.0),
+    operation_cost = ThreePartCost(LinearFunctionData(1400.0), 0.0, 4.0, 2.0),
     base_power = 1.0,
 )
 
diff --git a/test/test_function_data.jl b/test/test_function_data.jl
index aa87a9c4e0..806b238f8e 100644
--- a/test/test_function_data.jl
+++ b/test/test_function_data.jl
@@ -73,7 +73,7 @@ end
 end
 
 @testset "Test FunctionData piecewise point/slope conversion" begin
-    rng = Xoshiro(0)  # Set random seed for determinism
+    rng = Random.Xoshiro(0)  # Set random seed for determinism
     n_tests = 100
     n_points = 10
     for _ in 1:n_tests