Add tests to make sure all projections work

test/projection_math.jl

@@ -1,4 +1,33 @@
+using Makie
+
 @testset "Projection math" begin
-    @test eltype(Makie.rotationmatrix_x(1)) == Float64
-    @test eltype(Makie.rotationmatrix_x(1f0)) == Float32
+    @testset "Rotation matrix" begin
+        @test eltype(Makie.rotationmatrix_x(1)) == Float64
+        @test eltype(Makie.rotationmatrix_x(1f0)) == Float32
+    end
+    @testset "Projection between spaces in 3D" begin
+        # Set up an LScene and some points there
+        sc = Scene(size = (650, 400), camera = cam3d!)
+        corner_points_px = [Point3f(0, 0, 0), Point3f(650, 400, 0)]
+
+        @testset "Clip space and pixel space equivalence" begin
+            far_bottom_left_clip = Point3f(-1)
+            near_top_right_clip = Point3f(1)
+
+            fbl_px = Makie.project(sc, :clip, :pixel, far_bottom_left_clip)
+            ntr_px = Makie.project(sc, :clip, :pixel, near_top_right_clip)
+            @test Point2f(fbl_px) == Point2f(0, 0)
+            @test Point2f(ntr_px) == Point2f(650, 400)
+        end
+
+        @testset "No warnings in projections between spaces" begin
+            for (source, dest) in unique(Iterators.product(Makie.spaces(), Makie.spaces()))
+                source == dest && continue
+                current_space_points = Makie.project.(sc, :pixel, source, corner_points_px)
+                @testset "$source → $dest" begin
+                    @test_nowarn Makie.project.(sc, source, dest, current_space_points)
+                end
+            end
+        end
+    end
 end