Add docs

tests/tests.nim

@@ -0,0 +1,38 @@
+# To run these tests, simply execute `nimble test`.
+
+import unittest
+import op
+
+test "Check OK":
+  let test = ok 1
+  check test.isOk == true
+
+test "Check fail":
+  let test = op.fail[int] "no data here"
+  check test.isOk == false
+
+test "Check proc results":
+  proc createValue: OP[string] =
+    let myString = "This is test code!"
+    ok myString
+  let data = createValue()
+  check data.isOk
+  check data.val == "This is test code!"
+
+test "Check failing proc":
+  proc someProc(): OP[int] =
+    result.fail "Not implemented!"
+
+  let data = someProc()
+  assert data.isOk == false
+  assert data.error == "Not implemented!"
+
+test "Check changing result":
+  proc checker(): OP[int] =
+    result = ok 42
+    # something happend here
+    result = result.fail "data got corrupted"
+
+  let data = checker()
+  check data.isOk == false
+  check data.error == "data got corrupted"