我正在尝试为返回 IO monad 的 haskell 函数编写 HUnit 测试,因为它们执行文件 I/O。有什么办法可以做到这一点吗?现在我正在尝试编写一个仅返回 Bool 的方法,这可以作为我的测试
combine :: FilePath -> FilePath -> Bool
combine fp1 fp2 = do
cs <- readFile fp1
let (_,y,z) = strToHuff cs
let _ = writeToFile fp2 z y
(a, b) <- readFromFile fp2
z == a && b == y
但这给了我以下错误:
FileWriter.hs:153:3: Couldn't match type ‘IO b0’ with ‘Bool’ …
Expected type: IO String -> (String -> IO b0) -> Bool
Actual type: IO String -> (String -> IO b0) -> IO b0
In a stmt of a 'do' block: cs <- readFile fp1
In the expression:
do { cs <- readFile fp1;
let (_, y, z) = strToHuff cs;
let _ = writeToFile "try1.txt" z y;
(a, b) <- readFromFile fp2;
.... }
In an equation for ‘combine’:
combine fp1 fp2
= do { cs <- readFile fp1;
let (_, y, z) = ...;
let _ = ...;
.... }
FileWriter.hs:157:3: Couldn't match expected type ‘IO b0’ with actual type ‘Bool’ …
In a stmt of a 'do' block: z == a && b == y
In the expression:
do { cs <- readFile fp1;
let (_, y, z) = strToHuff cs;
let _ = writeToFile "try1.txt" z y;
(a, b) <- readFromFile fp2;
.... }
In an equation for ‘combine’:
combine fp1 fp2
= do { cs <- readFile fp1;
let (_, y, z) = ...;
let _ = ...;
.... }
Compilation failed.
就像@user2407038 在评论中所说的以及在HUnit 用户手册 https://wiki.haskell.org/HUnit_1.0_User's_Guide#AssertionsHUnit 测试运行在IO monad https://hackage.haskell.org/package/HUnit-1.3.0.0/docs/Test-HUnit-Base.html#t:Assertion.
这是一个例子:
testFilesEqual = TestCase (do x <- readFile "a.txt"
y <- readFile "b.txt"
assertEqual "files not equal" x y)
# a.txt == b.txt
λ> runTestTT testFilesEqual
Cases: 1 Tried: 0 Errors: 0 Failures: 0
Counts {cases = 1, tried = 1, errors = 0, failures = 0}
# a.txt != b.txt
λ> runTestTT testFilesEqual
### Failure:
files not equal
expected: "hello\n"
but got: "world\n"
Cases: 1 Tried: 1 Errors: 0 Failures: 1
Counts {cases = 1, tried = 1, errors = 0, failures = 1}
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