Go Unit Testing

Unit Testing

Instructions for AI coding agents on automating unit test creation using consistent software testing patterns in this Go project.

• 1. Benefits
• 2. Principles
  • 2.1. FIRST
• 3. Patterns
  • 3.1. In-Got-Want
  • 3.2. Table-Driven Testing
  • 3.3. Data-Driven Testing (DDT)
  • 3.4. Arrange, Act, Assert (AAA)
  • 3.5. Test Fixtures
• 4. Workflow
• 5. Commands
• 6. Style Guide
• 7. Template
  • 7.1. File Header Template
  • 7.2. Table-Driven Test Template
  • 7.3. Test Fixture Template
  • 7.4. Error Test Template
  • 7.5. Boundary Value Test Template
  • 7.6. Data-Driven Test Template (JSON)
• 8. References

1. Benefits

• Readability

  Ensures high code quality and reliability. Tests are self-documenting, reducing cognitive load for reviewers and maintainers.

• Consistency

  Uniform structure across tests ensures predictable, familiar code that team members can navigate efficiently.

• Scalability

  Table-driven and data-driven approaches minimize boilerplate code when adding new test cases, making it simple to expand coverage.

• Debuggability

  Scoped traces and detailed assertion messages pinpoint failures quickly during continuous integration and local testing.

2. Principles

2.1. FIRST

The FIRST principles for unit testing focus on creating effective and maintainable tests.

• Fast

  Unit tests should execute quickly to provide rapid feedback during development and continuous integration.

• Independent

  Each unit test should be self-contained and not rely on the state or behavior of other tests.

• Repeatable

  Unit tests should produce deterministic results every time they are run, regardless of the environment or order of execution.

• Self-Validating

  Unit tests should have clear pass/fail outcomes without requiring manual inspection.

• Timely

  Unit tests should be written and executed early in the development process to catch issues as soon as possible.

3. Patterns

3.1. In-Got-Want

The In-Got-Want pattern structures each test case into three clear sections.

• In

  Defines the input parameters or conditions for the test.

• Got

  Captures the actual output or result produced by the code under test.

• Want

  Specifies the expected output or result that the test is verifying against.

3.2. Table-Driven Testing

Table-driven testing organizes test cases in a tabular format, allowing multiple scenarios to be defined concisely.

• Test Case Structure

  Each row in the table represents a distinct test case with its own set of inputs and expected outputs.

• Iteration

  The test framework iterates over each row, executing the same test logic with different data.

3.3. Data-Driven Testing (DDT)

Data-driven testing separates test data from test logic, enabling the same test logic to be executed with multiple sets of input data.

• External Data Sources

  Test data can be stored in external files (e.g., JSON, CSV) and loaded at runtime.

• Reusability

  The same test logic can be reused with different datasets, enhancing maintainability and coverage.

3.4. Arrange, Act, Assert (AAA)

The AAA pattern structures each test case into three clear phases.

• Arrange

  Set up the necessary preconditions and inputs for the test.

• Act

  Execute the function or method being tested.

• Assert

  Verify that the actual output matches the expected output.

3.5. Test Fixtures

Test fixtures provide a consistent and reusable setup and teardown mechanism for test cases.

• Setup

  Initialize common objects or state needed for multiple tests.

• Teardown

  Clean up resources or reset state after each test.

4. Workflow

1. Identify

   Identify new functions in pkg/ or internal/ (e.g., pkg/<package>/<file>.go).

2. Add/Create

   Create new tests in the same package (e.g., pkg/<package>/<file>_test.go).

3. Test Coverage Requirements

   Include comprehensive edge cases:

   • Coverage-guided cases
   • Boundary values (min/max limits, edge thresholds)
   • Empty/null inputs
   • Null pointers and invalid references
   • Overflow/underflow scenarios
   • Special cases (negative numbers, zero, special states)

4. Apply Templates

   Structure all tests using the template pattern.

5. Commands

6. Style Guide

• Test Framework

  Use the standard Go testing package.

• Include Imports

  Include testing and github.com/google/go-cmp/cmp for comparisons.

• Parallelism

  Use t.Parallel() to run tests in parallel.

• Test Organization

  Consolidate test cases for a single function into one TestXxx(t *testing.T) function using table-driven testing.

  This approach:

  • Eliminates redundant test function definitions
  • Simplifies maintenance by grouping related scenarios together
  • Reduces code duplication in setup and teardown phases
  • Makes it easier to add or modify test cases

• Assertions

  Use cmp.Equal for value comparisons and errors.Is for error checking.

7. Template

Use these templates for new unit tests. Replace placeholders with actual values.

7.1. File Header Template

// SPDX-License-Identifier: Apache-2.0

package <package>

import (
	"errors"
	"testing"

	"github.com/google/go-cmp/cmp"
)

7.2. Table-Driven Test Template

func Test<FunctionName>(t *testing.T) {
	t.Parallel()

	// In-Got-Want
	type in struct {
		/* input fields */
	}

	type want struct {
		/* expected output fields */
		err error
	}

	// Table-Driven Testing
	tests := []struct {
		name string
		in   in
		want want
	}{
		{
			name: "case-description-1",
			in: in{
				/* input values */
			},
			want: want{
				/* expected output */
				err: nil,
			},
		},
		{
			name: "case-description-2",
			in: in{
				/* input values */
			},
			want: want{
				/* expected output */
				err: nil, // or specific error
			},
		},
		// add more cases as needed
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			// Arrange
			// additional setup as needed

			// Act
			got, err := <Function>(tt.in.<input>)

			// Assert
			if !errors.Is(err, tt.want.err) {
				t.Errorf("<Function>() error = %v, want err %v", err, tt.want.err)
			}
			if !cmp.Equal(got, tt.want.<value>) {
				t.Errorf("<Function>(%+v) = %v, want %v", tt.in, got, tt.want.<value>)
			}
		})
	}
}

7.3. Test Fixture Template

// testFixture holds common test state and provides setup/teardown.
type testFixture struct {
	t      *testing.T
	// Add common fields for test state
	object *<Type>
}

// newTestFixture creates and initializes a test fixture.
func newTestFixture(t *testing.T) *testFixture {
	t.Helper()

	// Setup
	return &testFixture{
		t:      t,
		object: New<Type>(),
	}
}

// teardown cleans up resources after test completion.
func (f *testFixture) teardown() {
	f.t.Helper()

	// Teardown
	if f.object != nil {
		f.object.Close()
	}
}

func Test<FunctionName>WithFixture(t *testing.T) {
	t.Parallel()

	// Arrange
	f := newTestFixture(t)
	defer f.teardown()

	input := <input_value>

	// Act
	got, err := f.object.<Function>(input)

	// Assert
	if err != nil {
		t.Errorf("<Function>() unexpected error: %v", err)
	}
	if !cmp.Equal(got, <expected>) {
		t.Errorf("<Function>() = %v, want %v", got, <expected>)
	}
}

7.4. Error Test Template

func Test<FunctionName>Error(t *testing.T) {
	t.Parallel()

	// In-Got-Want
	type in struct {
		/* invalid input fields */
	}

	type want struct {
		err error
	}

	// Table-Driven Testing
	tests := []struct {
		name string
		in   in
		want want
	}{
		{
			name: "nil-input-returns-error",
			in: in{
				/* nil or invalid input */
			},
			want: want{
				err: resource.Err<ErrorName>,
			},
		},
		{
			name: "invalid-value-returns-error",
			in: in{
				/* invalid value */
			},
			want: want{
				err: resource.Err<ErrorName>,
			},
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			// Arrange
			// setup if needed

			// Act
			_, err := <Function>(tt.in.<input>)

			// Assert
			if !errors.Is(err, tt.want.err) {
				t.Errorf("<Function>() error = %v, want err %v", err, tt.want.err)
			}
		})
	}
}

7.5. Boundary Value Test Template

func Test<FunctionName>BoundaryValues(t *testing.T) {
	t.Parallel()

	// In-Got-Want
	type in struct {
		input <input_type>
	}

	type want struct {
		value <output_type>
		err   error
	}

	// Table-Driven Testing
	tests := []struct {
		name string
		in   in
		want want
	}{
		{
			name: "minimum-value",
			in:   in{input: <MIN_VALUE>},
			want: want{value: /* expected */, err: nil},
		},
		{
			name: "maximum-value",
			in:   in{input: <MAX_VALUE>},
			want: want{value: /* expected */, err: nil},
		},
		{
			name: "zero-value",
			in:   in{input: 0},
			want: want{value: /* expected */, err: nil},
		},
		{
			name: "negative-value",
			in:   in{input: -1},
			want: want{value: /* expected */, err: nil},
		},
		{
			name: "overflow-value",
			in:   in{input: math.MaxFloat64},
			want: want{value: 0, err: resource.ErrOverflow},
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			// Arrange
			// setup if needed

			// Act
			got, err := <Function>(tt.in.input)

			// Assert
			if !errors.Is(err, tt.want.err) {
				t.Errorf("<Function>() error = %v, want err %v", err, tt.want.err)
			}
			if !cmp.Equal(got, tt.want.value) {
				t.Errorf("<Function>(%v) = %v, want %v", tt.in.input, got, tt.want.value)
			}
		})
	}
}

7.6. Data-Driven Test Template (JSON)

import (
	"encoding/json"
	"os"
	"path/filepath"
	"testing"

	"github.com/google/go-cmp/cmp"
)

// testCase represents a single test case loaded from JSON.
type testCase struct {
	Name string `json:"name"`
	In   struct {
		Input <input_type> `json:"input"`
	} `json:"in"`
	Want struct {
		Expected <output_type> `json:"expected"`
	} `json:"want"`
}

// testData represents the JSON test data structure.
type testData struct {
	Tests []testCase `json:"tests"`
}

func Test<FunctionName>DataDriven(t *testing.T) {
	t.Parallel()

	// Load test data from JSON file
	testdataPath := filepath.Join("testdata", "<function>_test.json")
	data, err := os.ReadFile(testdataPath)
	if err != nil {
		t.Fatalf("failed to read test data: %v", err)
	}

	var td testData
	if err := json.Unmarshal(data, &td); err != nil {
		t.Fatalf("failed to parse test data: %v", err)
	}

	for _, tc := range td.Tests {
		t.Run(tc.Name, func(t *testing.T) {
			// Arrange
			input := tc.In.Input
			expected := tc.Want.Expected

			// Act
			got, err := <Function>(input)

			// Assert
			if err != nil {
				t.Errorf("<Function>() unexpected error: %v", err)
			}
			if !cmp.Equal(got, expected) {
				t.Errorf("<Function>(%v) = %v, want %v", input, got, expected)
			}
		})
	}
}

• tests/data/<function>_test.json

  JSON file containing test cases.

  {
    "tests": [
      {
        "name": "case-description-1",
        "in": {
          "input": <value>
        },
        "want": {
          "expected": <value>
        }
      },
      {
        "name": "case-description-2",
        "in": {
          "input": <value>
        },
        "want": {
          "expected": <value>
        }
      }
    ]
  }
  

8. References

• Go Testing package documentation.
• Google go-cmp package documentation.