re-organized pattern matching code

cfg/config.go

@@ -186,14 +186,15 @@ func (c *Config) ApplyDefaults() {
 	}
 }
 
-func (c *Config) PreparePattern() error {
-	PatternR, err := regexp.Compile(c.Pattern)
+func (c *Config) PreparePattern(pattern string) error {
+	PatternR, err := regexp.Compile(pattern)
 
 	if err != nil {
 		return errors.Unwrap(fmt.Errorf("Regexp pattern %s is invalid: %w", c.Pattern, err))
 	}
 
 	c.PatternR = PatternR
+	c.Pattern = pattern
 
 	return nil
 }

cfg/config_test.go

@@ -76,3 +76,28 @@ func TestPrepareSortFlags(t *testing.T) {
 		})
 	}
 }
+
+func TestPreparePattern(t *testing.T) {
+	var tests = []struct {
+		pattern string
+		wanterr bool
+	}{
+		{"[A-Z]+", false},
+		{"[a-z", true},
+	}
+
+	for _, tt := range tests {
+		testname := fmt.Sprintf("PreparePattern-pattern-%s-wanterr-%t", tt.pattern, tt.wanterr)
+		t.Run(testname, func(t *testing.T) {
+			c := Config{}
+
+			err := c.PreparePattern(tt.pattern)
+
+			if err != nil {
+				if !tt.wanterr {
+					t.Errorf("PreparePattern returned error: %s", err)
+				}
+			}
+		})
+	}
+}