Improve axis label in case of empty name or unit

- Remove leading white space when a unit was present but no axis name
- Use an empty label if no axis name was specified and the unit was an empty string
- Extracted axis label generator to own method for easier overwrite

chartfx-chart/src/main/java/io/fair_acc/chartfx/axes/spi/AbstractAxisParameter.java

@@ -1081,17 +1081,22 @@ protected void updateAxisLabel() {
         if (state.isClean(ChartBits.AxisLabelText)) {
             return;
         }
+        getAxisLabel().setText(generateAxisLabelText());
+        state.clear(ChartBits.AxisLabelText);
+    }
+
+    /* visible for testing */ protected String generateAxisLabelText() {
         String unit = getUnit();
-        String prefix = MetricPrefix.getShortPrefix(getUnitScaling());
+        String unitPrefix = MetricPrefix.getShortPrefix(getUnitScaling());
 
-        if (unit == null && PropUtil.isNullOrEmpty(prefix)) {
-            getAxisLabel().setText(getName());
+        if (PropUtil.isNullOrEmpty(unit) && PropUtil.isNullOrEmpty(unitPrefix)) {
+            return getName();
         } else {
             unit = (unit == null) ? "" : unit;
-            prefix = (prefix == null) ? "" : prefix;
-            getAxisLabel().setText(getName() + " [" + prefix + unit + "]");
+            unitPrefix = (unitPrefix == null) ? "" : unitPrefix;
+            String namePart = PropUtil.isNullOrEmpty(getName()) ? "" : getName() + " ";
+            return namePart + "[" + unitPrefix + unit + "]";
         }
-        state.clear(ChartBits.AxisLabelText);
     }
 
     protected void updateScaleAndUnitPrefix() {

chartfx-chart/src/test/java/io/fair_acc/chartfx/axes/spi/AbstractAxisParameterTests.java

@@ -136,7 +136,7 @@ void testBasicGetterSetters() {
         assertEquals("axis name2", axis.getAxisLabel().getText());
 
         axis.set("axis name2", "", -3.0, +3.0);
-        assertEquals("axis name2 []", axis.getAxisLabel().getText());
+        assertEquals("axis name2", axis.getAxisLabel().getText());
 
         axis.set("axis name2", "axis unit2");
         assertEquals("axis name2", axis.getName());

chartfx-chart/src/test/java/io/fair_acc/chartfx/axes/spi/DefaultNumericAxisTests.java

@@ -1,12 +1,14 @@
 package io.fair_acc.chartfx.axes.spi;
 
-import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.stream.Stream;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.function.ThrowingSupplier;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -93,4 +95,25 @@ public void parameterTests() {
         tickValues.clear();
         axis.calculateMinorTickValues(tickValues);
     }
+
+    @ParameterizedTest
+    @MethodSource("testAxisLabelTextProvider")
+    void testAxisLabelText(String expected, String name, String unit, double unitScaling) throws Exception {
+        final DefaultNumericAxis axis = new DefaultNumericAxis(name, unit);
+        axis.setUnitScaling(unitScaling);
+        assertEquals(expected, axis.generateAxisLabelText());
+    }
+
+    private static Stream<Arguments> testAxisLabelTextProvider() { // NOPMD -- is used in annotation /not detected by PMD
+        return Stream.of(
+                Arguments.arguments("axis name [axis unit]", "axis name", "axis unit", 1.),
+                Arguments.arguments("DeviceA [V]", "DeviceA", "V", 1.),
+                Arguments.arguments("DeviceA [mV]", "DeviceA", "V", 0.001),
+                Arguments.arguments("axis name", "axis name", null, 1.),
+                Arguments.arguments("[V]", "", "V", 1.),
+                Arguments.arguments("[V]", null, "V", 1.),
+                Arguments.arguments("", "", "", 1.),
+                Arguments.arguments(null, null, null, 1.)
+                );
+    }
 }