Add generated CLDR test data for locale display names for ICU v73-75 (#…

…286)

* Add generated CLDR test data for locale display names for ICU v73-75

* Improve docs about test generation, esp for locale display names

testgen/README.md

@@ -1,4 +1,14 @@
-# testgen
+# testgen - Test Data Generators
+
+Test data generation is about converting test data from its original form into JSON conforming to a schema that we design for that functionality component.
+
+The process of test data generation (for a particular component of functionality) entails:
+
+1. Finding the original source test data
+2. Creating a JSON schema that is appropriate for the particular functionality component
+3. Creating code to convert the original format to the new JSON format to be used by DDT
+
+## Usage
 
 Generate all test data:
 ```sh
@@ -14,3 +24,36 @@ Show all options:
 ```sh
 python testdata_gen.py --help
 ```
+
+## Prerequisites
+
+For some components, obtaining the original source test data requires manual work.
+The following document some of those manual steps required:
+
+### Locale Display Names (aka lang_names)
+
+The code to generate locale display names test data was
+[merged into CLDR after CLDR v45](https://github.com/unicode-org/cldr/pull/3728).
+
+In order to retroactively apply the test generator code to older versions of CLDR,
+the following steps can be employed for a specific version of CLDR:
+
+1. checkout snapshot of old CLDR version
+    ```
+    git co release-43 -b release-43-ddt-datagen
+    ```
+2. pull backwards the current desired version of the test data generator
+    ```
+    git checkout main -- tools/cldr-code/src/main/java/org/unicode/cldr/tool/GenerateLocaleIDTestData.java
+    ```
+3. compile and run the generator from the right spot
+    ```
+    pushd tools/cldr-code
+    mvn compile exec:java -DCLDR_DIR=/usr/local/google/home/elango/oss/cldr/mine/src -Dexec.mainClass=org.unicode.cldr.tool.GenerateLocaleIDTestData
+    popd
+    ```
+4. copy the generated test data file to the Conformance repo
+    ```
+    cp ./common/testData/localeIdentifiers/localeDisplayName.txt ~/oss/conformance/testgen/icu73
+    ```
+