Add Unitful tests for constant extrapolation

test/extrapolation_tests.jl

@@ -1,6 +1,7 @@
 using DataInterpolations, Test
 using ForwardDiff
 using QuadGK
+using Unitful
 
 function test_extrapolation(method, u, t)
     @testset "Extrapolation errors" begin
@@ -43,6 +44,48 @@ function test_extrapolation(method, u, t)
     end
 end
 
+@testset "Constant Interpolation with Unitful" begin
+    t_un = [1.0, 2.0]u"s"
+    u_un = [1.0, 2.0]u"m"
+
+    for extrapolation_type in [ExtrapolationType.Constant, ExtrapolationType.Linear]
+        # Left extrapolation
+        A = ConstantInterpolation(u_un, t_un; extrapolation_left = extrapolation_type)
+        t_eval = 0.0u"s"
+        @test A(t_eval) == 1.0u"m"
+
+        # Right extrapolation
+        A = ConstantInterpolation(u_un, t_un; extrapolation_right = extrapolation_type)
+        t_eval = 3.0u"s"
+        @test A(t_eval) == 2.0u"m"
+    end
+end
+
+@testset "Linear Interpolation with Unitful" begin
+    t_un = [1.0, 2.0]u"s"
+    u_un = [1.0, 2.0]u"m"
+
+    # Left constant extrapolation
+    A = LinearInterpolation(u_un, t_un; extrapolation_left = ExtrapolationType.Constant)
+    t_eval = 0.0u"s"
+    @test A(t_eval) == 1.0u"m"
+
+    # Right constant extrapolation
+    A = LinearInterpolation(u_un, t_un; extrapolation_right = ExtrapolationType.Constant)
+    t_eval = 3.0u"s"
+    @test A(t_eval) == 2.0u"m"
+
+    # Left linear extrapolation
+    A = LinearInterpolation(u_un, t_un; extrapolation_left = ExtrapolationType.Linear)
+    t_eval = 0.0u"s"
+    @test A(t_eval) == 0.0u"m"
+
+    # Right constant extrapolation
+    A = LinearInterpolation(u_un, t_un; extrapolation_right = ExtrapolationType.Linear)
+    t_eval = 3.0u"s"
+    @test A(t_eval) == 3.0u"m"
+end
+
 @testset "Linear Interpolation" begin
     u = [1.0, 2.0]
     t = [1.0, 2.0]