CSHARP-5000: Convert read/write concern spec tests to unified test format (#1640)

Author: BorisDog

specifications/read-write-concern/tests/README.md

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+# Read and Write Concern Tests
+
+The YAML and JSON files in this directory tree are platform-independent tests that drivers can use to prove their
+conformance to the Read and Write Concern specification.
+
+## Version
+
+Files in the "specifications" repository have no version scheme. They are not tied to a MongoDB server version.
+
+## Format
+
+### Connection String
+
+These tests are designed to exercise the connection string parsing related to read concern and write concern.
+
+Each YAML file contains an object with a single `tests` key. This key is an array of test case objects, each of which
+have the following keys:
+
+- `description`: A string describing the test.
+- `uri`: A string containing the URI to be parsed.
+- `valid:`: a boolean indicating if parsing the uri should result in an error.
+- `writeConcern:` A document indicating the expected write concern.
+- `readConcern:` A document indicating the expected read concern.
+
+If a test case includes a null value for one of these keys, or if the key is missing, no assertion is necessary. This
+both simplifies parsing of the test files and allows flexibility for drivers that might substitute default values
+*during* parsing.
+
+### Document
+
+These tests are designed to ensure compliance with the spec in relation to what should be sent to the server.
+
+Each YAML file contains an object with a single `tests` key. This key is an array of test case objects, each of which
+have the following keys:
+
+- `description`: A string describing the test.
+- `valid:`: a boolean indicating if the write concern created from the document is valid.
+- `writeConcern:` A document indicating the write concern to use.
+- `writeConcernDocument:` A document indicating the write concern to be sent to the server.
+- `readConcern:` A document indicating the read concern to use.
+- `readConcernDocument:` A document indicating the read concern to be sent to the server.
+- `isServerDefault:` Indicates whether the read or write concern is considered the server's default.
+- `isAcknowledged:` Indicates if the write concern should be considered acknowledged.
+
+### Operation
+
+These tests check that the default write concern is omitted in operations.
+
+The tests utilize the [Unified Test Format](../../unified-test-format/unified-test-format.md).
+
+#### Use as unit tests
+
+Testing whether a URI is valid or not should simply be a matter of checking whether URI parsing raises an error or
+exception. Testing for emitted warnings may require more legwork (e.g. configuring a log handler and watching for
+output).