Add test for undefined behavior of unsafe_trunc

test/common.jl

@@ -389,3 +389,26 @@ function test_rand(TX::Type)
         @test size(a) == (3, 5)
     end
 end
+
+# issue #288
+# The following needs to be outside of `@testset` to reproduce the issue.
+@inline _to_fixed(::Val, x) = x % Q0f7
+@inline _to_fixed(::Val{:Q0f15}, x) = x % Q0f15
+@inline _to_normed(::Val, x) = x % N0f8
+@inline _to_normed(::Val{:N0f16}, x) = x % N0f16
+function _issue288(::Type{Fixed})
+    buf = IOBuffer()
+    for sym in (:Q0f7, :Q0f15)
+        show(buf, _to_fixed(Val(sym), -1.0))
+        print(buf, " ")
+    end
+    return String(take!(buf))
+end
+function _issue288(::Type{Normed})
+    buf = IOBuffer()
+    for sym in (:N0f8, :N0f16)
+        show(buf, _to_normed(Val(sym), 1.0))
+        print(buf, " ")
+    end
+    return String(take!(buf))
+end

test/fixed.jl

@@ -282,6 +282,14 @@ end
 
     @test -1 % Q0f7 === Q0f7(-1)
     @test -2 % Q0f7 === Q0f7(0)
+
+    # issue #288
+    if _issue288(Fixed) == "-1.0Q0f7 -1.0Q0f15 " # just leave it in the report
+        @test _issue288(Fixed) == "-1.0Q0f7 -1.0Q0f15 "
+    else
+        @test_broken _issue288(Fixed) == "-1.0Q0f7 -1.0Q0f15 "
+        @warn "broken result: " * repr(_issue288(Fixed))
+    end
 end
 
 @testset "neg" begin

test/normed.jl

@@ -279,6 +279,14 @@ end
     # issue #211
     @test big"1.2" % N0f8 === 0.196N0f8
     @test reinterpret(BigFloat(0x0_01234567_89abcdef) % N63f1) === 0x01234567_89abcdef
+
+    # issue #288
+    if _issue288(Normed) == "1.0N0f8 1.0N0f16 " # just leave it in the report
+        @test _issue288(Normed) == "1.0N0f8 1.0N0f16 "
+    else
+        @test_broken _issue288(Normed) == "1.0N0f8 1.0N0f16 "
+        @warn "broken result: " * repr(_issue288(Normed))
+    end
 end
 
 @testset "arithmetic" begin