DRIVERS-2505 clarify type expectations in prose test (#1409)

* clarify type expectation applies to encoded BSON type

The BSON type differs from the input type. The input type may be a language native type (e.g. an Int64 wrapper class).

* use long and int in clarification

int32/int64 handling may be more likely to cause confusion in implementation

* add note clarifying returned type may not match input type

Author: kevinAlbs

source/client-side-encryption/tests/README.rst

@@ -2807,7 +2807,7 @@ Each test listed in the cases below must pass for all supported data types unles
 
 Case 1: can decrypt a payload
 `````````````````````````````
-Use ``clientEncryption.encrypt()`` to encrypt the value 6. Ensure the type matches with the type of the encrypted field. For example, if the encrypted field is ``encryptedDoubleNoPrecision`` encrypt the double value 6.0.
+Use ``clientEncryption.encrypt()`` to encrypt the value 6. Ensure the encoded BSON type matches the type of the encrypted field. For example, if the encrypted field is ``encryptedLong`` encrypt the 64-bit BSON long value 6, not the 32-bit BSON int value 6.
 
 Store the result in ``insertPayload``.
 
@@ -2823,6 +2823,11 @@ Encrypt with the matching ``RangeOpts`` listed in `Test Setup: RangeOpts`_ and t
 
 Use ``clientEncryption`` to decrypt ``insertPayload``. Assert the returned value equals 6.
 
+.. note::
+
+   The type returned by ``clientEncryption.decrypt()`` may differ from the input type to ``clientEncryption.encrypt()`` depending on how the driver unmarshals BSON numerics to language native types.
+   Example: a driver may unmarshal a BSON long to a numeric type that does not distinguish between int64 and int32.
+
 Case 2: can find encrypted range and return the maximum 
 ```````````````````````````````````````````````````````
 Use ``clientEncryption.encryptExpression()`` to encrypt this query: