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I S A M I N D S E T P R O P E R T Y - B A S E D T E S T I N G

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@whatyouhide

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No content

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Elixir

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T E S T I N G

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why do we test? no tests yes tests

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unit tests

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test "sorting" do assert sort([]) == [] assert sort([1, 2, 3]) == [1, 2, 3] assert sort([2, 1, 3]) == [1, 2, 3] end example-based

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table-based Input Output [] [] [1, 2, 3] [1, 2, 3] [2, 1, 3] [1, 2, 3]

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unit tests , but also

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P R O P E R T I E S

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hard to write , but...

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valid inputs properties of output testing framework

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github.com/whatyouhide/stream_data

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example time: sorting lists

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test "sorting" do assert sort([]) == [] assert sort([1, 2, 3]) == [1, 2, 3] assert sort([2, 1, 3]) == [1, 2, 3] end

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lists of integers

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it's a list has the same elements it's ordered

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check all list <- list_of(int()) do sorted = sort(list) assert is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

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check all list <- list_of(int()) do sorted = sort(list) assert is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

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check all list <- list_of(int()) do sorted = sort(list) assert is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

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check all list <- list_of(int()) do sorted = sort(list) assert is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

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check all list <- list_of(int()) do sorted = sort(list) assert is_list(sorted) assert same_elements?(list, sorted) assert ordered?(sorted) end

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def sort(list), do: list

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[32, 2, 44, -12] [1, 0] *shrinking

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P A T T E R N S

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circular code

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decode(encode(term)) == term

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property "encoding->decoding is circular" do check all bin <- binary() do encoded = Huffman.encode(bin) assert is_binary(encoded) assert Huffman.decode(encoded) == bin end end Huffman encoding

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oracle model

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my_code() == oracle_code()

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older system less performant implementation

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property "gives same results as Erlang impl" do check all bin <- binary() do assert Huffman.encode(bin) == :huffman.encode(bin) end end

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smoke tests https://www.youtube.com/watch?v=jvwfDdgg93E

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API: 200, 201, 400, 404 https://www.youtube.com/watch?v=jvwfDdgg93E

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https://www.youtube.com/watch?v=jvwfDdgg93E property "only expected codes are returned" do check all request <- request() do response = HTTP.perform(request) assert response.status in [200, 201, 400, 404] end end

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locally , CI

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if System.get_env("CI") == "true" do config :stream_data, max_runs: 500 else config :stream_data, max_runs: 25 end

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unit + properties

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R E A L - W O R L D E X A M P L E

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Redis parser

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continuation parser parse(bytes) {:ok, command} {:more, function}

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property "splitting commands at random" do check all cmd <- command(), split_cmd <- random_splits(cmd) do assert {:ok, _, ""} = parse_many(split_cmd) end end

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property "splitting commands at random" do check all cmd <- command(), split_cmd <- random_splits(cmd) do assert {:ok, _, ""} = parse_many(split_cmd) end end

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property "splitting commands at random" do check all cmd <- command(), split_cmd <- random_splits(cmd) do assert {:ok, _, ""} = parse_many(split_cmd) end end

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S T A T E F U L T E S T I N G

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model valid commands +

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model: state + state transformations

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commands: calls + preconditions

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bounded-size queue

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Max size model system

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•push(queue, value) •resize(queue, max_size) commands

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def push(model, _value), do: model def resize(_model, max_size), do: max_size

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push(queue, {:some, "value"}) push(queue, [123, 3.2]) resize(queue, 1) push(queue, %{})

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assert size(queue) <= model

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LevelDB

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17 (seventeen) calls 33 (thirty three) calls

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C O N C L U S I O N

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find obscure bugs reduce to minimal failing input find specification errors keep increasing input space

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v1.7

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use stream_data

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use property-based testing

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@whatyouhide github.com/whatyouhide/stream_data