check_gridded now enforces unique knots

Author: mkitti

src/gridded/gridded.jl

@@ -48,7 +48,7 @@ end
     end
     degree(flag) isa Union{NoInterp,Constant,Linear} || error("only Linear, Constant, and NoInterp supported, got $flag")
     length(k1) == 1 && error("dimensions of length 1 not yet supported")  # FIXME
-    issorted(k1) || error("knot-vectors must be sorted in increasing order")
+    issorted(k1) && allunique(k1) || error("knot-vectors must be unique and sorted in increasing order")
     check_gridded(getrest(itpflag), Base.tail(knots), Base.tail(axs))
 end
 check_gridded(::Any, ::Tuple{}, ::Tuple{}) = nothing

test/gridded/gridded.jl

@@ -88,4 +88,8 @@ using Interpolations, Test
 
     # trailing 1s, issue #301
     @test itp(1.8, 1) == itp(1.8)
+
+    # issue #395
+    knots = ([0.0,0.0,1.0],) # not unique
+    @test_throws ErrorException interpolate(knots, [1.0, 1.0, 2.0], Gridded(Linear()))
 end