Softmax regressor json keys unit tests added

test/classifier/softmax_regressor/softmax_regressor_json_keys_test.dart

@@ -0,0 +1,38 @@
+import 'package:ml_algo/src/classifier/softmax_regressor/softmax_regressor_json_keys.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('Softmax regressor json keys', () {
+    test('should contain a proper key for class names field', () {
+      expect(softmaxRegressorClassNamesJsonKey, 'CN');
+    });
+
+    test('should contain a proper key for fit intercept field', () {
+      expect(softmaxRegressorFitInterceptJsonKey, 'FI');
+    });
+
+    test('should contain a proper key for intercept scale field', () {
+      expect(softmaxRegressorInterceptScaleJsonKey, 'IS');
+    });
+
+    test('should contain a proper key for coefficients by classes field', () {
+      expect(softmaxRegressorCoefficientsByClassesJsonKey, 'CBC');
+    });
+
+    test('should contain a proper key for dtype field', () {
+      expect(softmaxRegressorDTypeJsonKey, 'DT');
+    });
+
+    test('should contain a proper key for link function feld', () {
+      expect(softmaxRegressorLinkFunctionJsonKey, 'LF');
+    });
+
+    test('should contain a proper key for positive label field', () {
+      expect(softmaxRegressorPositiveLabelJsonKey, 'PL');
+    });
+
+    test('should contain a proper key for negative label field', () {
+      expect(softmaxRegressorNegativeLabelJsonKey, 'NL');
+    });
+  });
+}