ICU-22917 Use the ICU version API. Add missing @test.

docs/processes/release/tasks/updating-measure-unit.md

@@ -36,24 +36,23 @@ Make sure `DRAFT_VERSION_SET` at top of
 is set correctly. \
 These are the ICU versions that have draft methods.
 
-In the same file set `ICU_CURRENT_VERSION` and `ICU_BACK_VERSION`. \
-
-**WARNING / TODO:** clarify what to set them to. I was unable to find documentation for that. \
-And I'm questioning if we need two versions. In fact I suspect that for 76 these were set incorrectly.
-
 The code is generated by running `MeasureUnitGeneratorTest.java` unit tests, which writes
 generated code to various file.
 
-1. Within **Eclipse**:
-   - Open `MeasureUnitGeneratorTest.java`, find the `generateUnitTestsUpdate` methods
-    and run it by clicking on the green play button on menu bar. \
-    Choose "JUnit Test" if asked.
-
-2. With **maven** (command line):
+1. With **maven** (command line):
    - Change folder to `{icuRoot}/icu4j`
    - run `mvn install -DskipTests -DskipITs`
    - run `mvn install -q -Dtest=MeasureUnitGeneratorTest -DgenerateMeasureUnitUpdate -f main/common_tests`
 
+2. Within **Eclipse**:
+   - Open `MeasureUnitGeneratorTest.java`, find the `generateUnitTestsUpdate` methods
+    and run it by clicking on the green play button on menu bar. \
+    Choose "JUnit Test" if asked. \
+    This will not generate the update, but it will run the test and create a "Run Configuration". \
+    Open it (Main menu -- "Run" -- "Run Configurations"), select the one named
+    `MeasureUnitGeneratorTest.generateUnitTestsUpdate`, go to the "Arguments" tab and add
+    `-DgenerateMeasureUnitUpdate` to the "VM Arguments" text area.
+
 Both methods will generate files with names starting with `genunits_` in `icu4j/main/common_tests/`. \
 The file names and the logging to the standard output will guide you.
 
@@ -101,7 +100,9 @@ code should be appended at some fixed place (details below).
 * **`measunit.cpp`:** replace range.
 * **`measfmttest.cpp`:** append the new generated method after the last
   `MeasureFormatTest::TestCompatible<version>()` method. \
-  Don't add it if it already exists.
+  Don't add it if it already exists. \
+  WARNING: here you should add the method in two places. The method proper, with code,
+  as generated, and the declaration in the class definition.
 * **`MeasureUnitGeneratorTest.java`:** append the new pairs of measure + version at
   the end of the `JAVA_VERSIONS` structure. \
   Don't add them if they already exist.

icu4j/main/common_tests/src/test/java/com/ibm/icu/dev/test/format/MeasureUnitCompatibleTest.java

@@ -2560,7 +2560,8 @@ public void TestCompatible74() {
         assertEquals("",  190, units.length);
     }
 
-   public void TestCompatible76() {
+    @Test
+    public void TestCompatible76() {
         MeasureUnit[] units = {
                 MeasureUnit.G_FORCE,
                 MeasureUnit.METER_PER_SECOND_SQUARED,
@@ -2755,7 +2756,7 @@ public void TestCompatible76() {
                 MeasureUnit.TABLESPOON,
                 MeasureUnit.TEASPOON,
         };
-        assertEquals("",  193, units.length);
+        assertEquals("",  192, units.length);
     }
 
    /*

icu4j/main/common_tests/src/test/java/com/ibm/icu/dev/test/format/MeasureUnitGeneratorTest.java

@@ -31,6 +31,7 @@
 import com.ibm.icu.impl.Pair;
 import com.ibm.icu.util.MeasureUnit;
 import com.ibm.icu.util.NoUnit;
+import com.ibm.icu.util.VersionInfo;
 
 /**
  * This is not a real test class. It is only used to
@@ -67,11 +68,6 @@ public int compareTo(OrderedPair<F, S> other) {
         }
     }
 
-    // TODO: what should these two version be? Should they in fact be the same?
-    // Can we take the version from `VersionInfo.ICU_VERSION.getMajor()`?
-    private static final String ICU_CURRENT_VERSION = "76";
-    private static final String ICU_BACK_VERSION = "74";
-
     private static final HashSet<String> DRAFT_VERSION_SET = new HashSet<>();
 
     private static final HashSet<String> TIME_CODES = new HashSet<>();
@@ -322,16 +318,17 @@ public void generateUnitTestsUpdate() throws IOException {
         // docs/processes/release/tasks/updating-measure-unit.md
         // use this test to run each of the following in succession
         if (System.getProperty("generateMeasureUnitUpdate") != null) {
+            final String icuVersion = Integer.toString(VersionInfo.ICU_VERSION.getMajor());
             System.out.println();
             System.out.println("WARNING: open the pairs of files listed below and copy code fragments, not full files!");
             System.out.println("Some kind of diff tool / editor would work best.");
 
-            generateConstants(ICU_CURRENT_VERSION); // update generated MeasureUnit constants
-            generateBackwardCompatibilityTest(ICU_CURRENT_VERSION); // create TestCompatible<icu_ver>
-            generateCXXHConstants(ICU_CURRENT_VERSION); // update generated createXXX methods
+            generateConstants(icuVersion); // update generated MeasureUnit constants
+            generateBackwardCompatibilityTest(icuVersion); // create TestCompatible<icu_ver>
+            generateCXXHConstants(icuVersion); // update generated createXXX methods
             generateCXXConstants(); // update generated code
-            generateCXXBackwardCompatibilityTest(ICU_BACK_VERSION); // create TestCompatible<icu_ver>
-            updateJAVAVersions(ICU_BACK_VERSION); // JAVA_VERSIONS
+            generateCXXBackwardCompatibilityTest(icuVersion); // create TestCompatible<icu_ver>
+            updateJAVAVersions(icuVersion); // JAVA_VERSIONS
         }
     }
 
@@ -695,6 +692,7 @@ private static void generateBackwardCompatibilityTest(String version) throws IOE
         try (PrintStream out = createAndStartOutputFile(fullOutputPath)) {
             Map<String, MeasureUnit> seen = new HashMap<>();
             out.println();
+            out.printf("    @Test\n");
             out.printf("    public void TestCompatible%s() {\n", version.replace(".", "_"));
             out.println("        MeasureUnit[] units = {");
             TreeMap<String, List<MeasureUnit>> allUnits = getAllUnits();