Add spec file for interpolate

spec/interpolate_spec.lua

@@ -0,0 +1,33 @@
+local vips = require "vips"
+
+-- test image interpolation
+describe("image interpolation", function()
+    setup(function()
+        -- vips.log.enable(true)
+    end)
+
+    it("can rotate an image using nearest interpolator", function()
+        local interpolate = vips.Interpolate.new_from_name("nearest")
+        local original = {
+            { 1, 2, 3 },
+            { 4, 5, 6 },
+            { 7, 8, 9 },
+        }
+        local rotated = {
+            { 0.0, 0.0, 1.0, 0.0 },
+            { 0.0, 0.0, 1.0, 2.0 },
+            { 0.0, 7.0, 5.0, 3.0 },
+            { 0.0, 8.0, 9.0, 6.0 }
+        }
+        local im = vips.Image.new_from_array(original)
+        local rot = im:rotate(45, { interpolate = interpolate })
+        assert.are.equal(rot:width(), 4)
+        assert.are.equal(rot:height(), 4)
+        assert.are.equal(rot:bands(), 1)
+        for x = 1, 4 do
+            for y = 1, 4 do
+                assert.are_equal(rot(x - 1, y - 1), rotated[y][x])
+            end
+        end
+    end)
+end)