Add tests

src/linear_algebra.jl

@@ -251,7 +251,7 @@ function operate(::typeof(*), x::LinearAlgebra.Transpose{<:Any, <:AbstractVector
         throw(DimensionMismatch("first array has length $(lx) which does not match the length of the second, $(length(y))."))
     end
     if iszero(lx)
-        return promote_operation(add_mul, eltype(x), eltype(y))
+        return zero(promote_operation(add_mul, eltype(x), eltype(y)))
     end
 
     # We need a buffer to hold the intermediate multiplication.

test/matmul.jl

@@ -58,6 +58,17 @@ end
         B = zeros(2, 2)
         err = DimensionMismatch("Cannot sum matrices of size `(1, 1)` and size `(2, 2)`, the size of the two matrices must be equal.")
         @test_throws err MA.@rewrite A + B
+        x = ones(1)
+        y = ones(2)
+        err = DimensionMismatch("first array has length 1 which does not match the length of the second, 2.")
+        @test_throws err MA.operate(*, x', y)
+        @test_throws err MA.operate(*, LinearAlgebra.transpose(x), y)
+        err = DimensionMismatch("matrix A has dimensions (2,2), vector B has length 1")
+        @test_throws err MA.operate(*, x', B)
+        a = zeros(0)
+        @test iszero(@inferred MA.operate(LinearAlgebra.dot, a, a))
+        @test iszero(@inferred MA.operate(*, a', a))
+        @test iszero(@inferred MA.operate(*, LinearAlgebra.transpose(a), a))
     end
 end